Using the method of integration, find the area of the triangular

Using integration, find the area bounded by the curve x2 = 4y and the line x = 4y – 2.


The shaded area OBAO represents the area bounded by the curve x2 = 4y and the line x = 4y – 2.


Let A and B be the points of intersection of the line and parabola.
Co-ordinates of point A are open parentheses negative 1 comma space 1 fourth close parentheses. space Co-ordinates of point B are (2, 1).
Area OBAO = Area OBCO + Area OACO   ...(1)
Area OBCO = 
equals integral subscript 0 superscript 2 fraction numerator straight x plus 2 over denominator 4 end fraction dx minus integral subscript 0 superscript 2 straight x squared over 4 dx
equals 1 fourth open square brackets straight x squared over 2 plus 2 straight x close square brackets subscript 0 superscript 2 minus 1 fourth open square brackets straight x cubed over 3 close square brackets subscript 0 superscript 2
equals 1 fourth open square brackets 2 plus 4 close square brackets minus 1 fourth open square brackets 8 over 3 close square brackets
equals 3 over 2 minus 2 over 3 equals 5 over 6
Area OACO = 
  equals integral subscript negative 1 end subscript superscript 0 fraction numerator straight x plus 2 over denominator 4 end fraction dx minus integral subscript negative 1 end subscript superscript 0 straight x squared over 4 dx
equals 1 fourth open square brackets straight x squared over 2 plus 2 straight x close square brackets subscript negative 1 end subscript superscript 0 space minus space 1 fourth open square brackets straight x cubed over 3 close square brackets subscript negative 1 end subscript superscript 0
equals 1 fourth open square brackets negative fraction numerator left parenthesis negative 1 right parenthesis squared over denominator 2 end fraction minus 2 left parenthesis negative 1 right parenthesis close square brackets minus 1 fourth open square brackets negative open parentheses negative 1 close parentheses cubed over 3 close square brackets
equals 1 fourth open square brackets negative 1 half plus 2 close square brackets minus 1 fourth open square brackets 1 third close square brackets
equals 3 over 8 minus 1 over 12 equals 7 over 24
Therefore, required area = open parentheses 5 over 6 plus 7 over 24 close parentheses space equals 9 over 8 sq. units

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Using integration, find the area of the region enclosed between the two circles:
straight x squared plus straight y squared space equals space 4 space and space left parenthesis straight x minus 2 right parenthesis squared plus straight y squared space equals space 4.


Given equations of the circles are:
straight x squared plus straight y squared space equals space 4 space space space... left parenthesis 1 right parenthesis
left parenthesis straight x minus 2 right parenthesis squared plus straight y squared space equals space 4 space... left parenthesis 2 right parenthesis
Equation (1) is a circle with centre O at the origin and radius 2. Equation (2) is a circle with centre C(2, 0) and radius 2.
Solving (1) and (2), we have:
left parenthesis straight x minus 2 right parenthesis squared plus straight y squared space equals space straight x squared plus straight y squared
straight x squared minus 4 straight x plus 4 plus straight y squared space equals space straight x squared plus straight y squared
straight x space equals space 1
This gives straight y equals plus-or-minus square root of 3
Thus, the points of intersection of the given circles are straight A open parentheses 1 comma space square root of 3 close parentheses space and space straight A apostrophe left parenthesis 1 comma space minus square root of 3 right parenthesis space as space shown space in space the space figure. space

Required area
 = Area of the region OACA'O
 = 2[area of the region ODCAO] 
 =2[area of the region ODAO + area of the region DCAD]
equals 2 open square brackets integral subscript 0 superscript 1 ydx plus integral subscript 1 superscript 2 ydx close square brackets
equals 2 open square brackets integral subscript 0 superscript 1 square root of 4 minus left parenthesis straight x minus 2 right parenthesis squared end root dx plus integral subscript 1 superscript 2 square root of 4 minus straight x squared end root dx close square brackets
equals 2 open square brackets 1 half left parenthesis straight x minus 2 right parenthesis square root of 4 minus left parenthesis straight x minus 2 right parenthesis squared end root plus 1 half cross times 4 sin to the power of negative 1 end exponent open parentheses fraction numerator straight x minus 2 over denominator 2 end fraction close parentheses close square brackets subscript 0 superscript 1 plus 2 open square brackets 1 half straight x square root of 4 minus straight x squared end root plus 1 half cross times 4 sin to the power of negative 1 end exponent straight x over 2 close square brackets subscript 1 superscript 2
equals open square brackets left parenthesis straight x minus 2 right parenthesis square root of 4 minus left parenthesis straight x minus 2 right parenthesis squared end root plus 4 sin to the power of negative 1 end exponent open parentheses fraction numerator straight x minus 2 over denominator 2 end fraction close parentheses close square brackets subscript 0 superscript 1 plus open square brackets straight x square root of 4 minus straight x squared end root plus 4 sin to the power of negative 1 end exponent straight x over 2 close square brackets subscript 1 superscript 2
equals open square brackets negative square root of 3 plus 4 sin to the power of negative 1 end exponent open parentheses fraction numerator negative 1 over denominator 2 end fraction close parentheses minus 4 sin to the power of negative 1 end exponent left parenthesis negative 1 right parenthesis close square brackets plus open square brackets 4 sin to the power of negative 1 end exponent 1 minus square root of 3 minus 4 sin to the power of negative 1 end exponent 1 half close square brackets
equals open square brackets open parentheses negative square root of 3 minus 4 cross times straight pi over 6 close parentheses plus 4 cross times straight pi over 2 close square brackets plus open square brackets 4 cross times straight pi over 2 minus square root of 3 minus 4 cross times straight pi over 6 close square brackets
equals fraction numerator 8 straight pi over denominator 3 end fraction minus 2 square root of 3


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Sketch the region bounded by the curves straight y equals square root of 5 minus straight x squared end root space and space straight y space equals open vertical bar straight x minus 1 close vertical bar and find its area using integration. 


Consider the given equation. 
straight y equals square root of 5 minus straight x squared end root
This equation represents a semicircle with centre at the origin and radius  = square root of 5 space units
Given that the region is bounded by the above semicircle and the line straight y equals open vertical bar straight x minus 1 close vertical bar
Let us find the point of intersection of the given curve meets the line straight y equals open vertical bar straight x minus 1 close vertical bar
rightwards double arrow square root of 5 minus straight x squared end root space equals space open vertical bar straight x minus 1 close vertical bar
Squaring both the sides, we have,

5 minus straight x squared space equals open vertical bar straight x minus 1 close vertical bar squared
rightwards double arrow 5 minus straight x squared space equals space straight x squared plus 1 minus 2 straight x
rightwards double arrow 2 straight x squared minus 2 straight x minus 5 plus 1 space equals space 0
rightwards double arrow 2 straight x squared minus 2 straight x minus 4 space equals space 0
rightwards double arrow straight x squared minus straight x minus 2 space equals 0
rightwards double arrow space straight x squared minus 2 straight x plus straight x minus 2 space equals 0
rightwards double arrow straight x left parenthesis straight x minus 2 right parenthesis plus 1 left parenthesis straight x minus 2 right parenthesis equals 0
rightwards double arrow left parenthesis straight x plus 1 right parenthesis thin space left parenthesis straight x minus 2 right parenthesis space equals space 0
rightwards double arrow straight x space equals negative 1 comma space straight x space equals space 2
When space straight x space equals space minus 1 comma space space straight y space equals space 2
When space straight x space equals space 2 comma space space straight y space equals space 1
Consider the following figure
Thus the intersection points are 1,2 and 2,1 ( ) ( ) Consider the following sketch of the bounded region.


Required Area, straight A space equals space integral subscript negative 1 end subscript superscript 2 left parenthesis straight y subscript 2 minus straight y subscript 1 right parenthesis dx space
equals integral subscript negative 1 end subscript superscript 1 space open square brackets square root of 5 minus straight x squared end root plus left parenthesis straight x minus 1 right parenthesis close square brackets dx space plus space integral subscript 1 superscript 2 space open square brackets square root of 5 minus straight x squared end root minus left parenthesis straight x minus 1 right parenthesis close square brackets dx
equals integral subscript negative 1 end subscript superscript 1 space square root of 5 minus straight x squared end root dx plus integral subscript negative 1 end subscript superscript 1 xdx space minus integral subscript negative 1 end subscript superscript 1 dx space plus space integral subscript 1 superscript 2 square root of 5 minus straight x squared end root dx minus integral subscript 1 superscript 2 xdx plus integral subscript 1 superscript 2 dx
equals open square brackets straight x over 2 square root of 5 minus straight x squared end root plus 5 over 2 sin to the power of negative 1 end exponent open parentheses fraction numerator straight x over denominator square root of 5 end fraction close parentheses close square brackets subscript negative 1 end subscript superscript 1 space plus space open parentheses straight x squared over 2 close parentheses subscript negative 1 end subscript superscript 1 space minus left parenthesis straight x right parenthesis subscript negative 1 end subscript superscript 1 plus open square brackets straight x over 2 square root of 5 minus straight x squared end root plus 5 over 2 sin to the power of negative 1 end exponent open parentheses fraction numerator straight x over denominator square root of 5 end fraction close parentheses close square brackets subscript 1 superscript 2
minus open parentheses straight x squared over 2 close parentheses subscript 1 superscript 2 space plus left parenthesis straight x right parenthesis subscript 1 superscript 2
equals 5 over 2 sin to the power of negative 1 end exponent open parentheses fraction numerator 1 over denominator square root of 5 end fraction close parentheses plus 5 over 2 sin to the power of negative 1 end exponent open parentheses fraction numerator 2 over denominator square root of 5 end fraction close parentheses minus 1 half

Required space Area space equals open square brackets 5 over 2 sin to the power of negative 1 end exponent open parentheses fraction numerator 1 over denominator square root of 5 end fraction close parentheses plus 5 over 2 sin to the power of negative 1 end exponent open parentheses fraction numerator 2 over denominator square root of 5 end fraction close parentheses minus 1 half close square brackets sq. space units



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Using integration, find the area of the region bounded by the triangle whose vertices are (-1, 2), (1, 5) and (3, 4).


Consider the vertices, A(-1, 2), B(1, 5) and C(3, 4).
Let us find the equation of the sides of the triangle increment ABC.
Thus, the equation of AB is:

fraction numerator straight y minus 5 over denominator 5 minus 2 end fraction space equals space fraction numerator straight x minus 1 over denominator 1 plus 1 end fraction
rightwards double arrow 3 straight x minus 2 straight y plus 7 space equals space 0
Similarly comma space the space equation space of space BC space is colon
fraction numerator straight y minus 4 over denominator 4 minus 5 end fraction equals fraction numerator straight x minus 3 over denominator 3 minus 1 end fraction
rightwards double arrow straight x plus 2 straight y minus 11 space equals 0
Also comma space the space equation space of space CA space is colon
fraction numerator straight y minus 4 over denominator 4 minus 2 end fraction space equals fraction numerator straight x minus 3 over denominator 3 plus 1 end fraction
rightwards double arrow straight x minus 2 straight y plus 5 space equals 0


Now the area of increment ABC = Area of increment ADB + Area of increment BDC

therefore space Area space of space increment ADB space equals space integral subscript negative 1 end subscript superscript 1 open square brackets fraction numerator 3 straight x plus 7 over denominator 2 end fraction minus fraction numerator straight x plus 5 over denominator 2 end fraction close square brackets dx

Similarly comma space Area space of space increment BDC equals space integral subscript 1 superscript 3 open square brackets fraction numerator 11 minus straight x over denominator 2 end fraction minus fraction numerator straight x plus 5 over denominator 2 end fraction close square brackets dx
Thus comma space Area space of space increment ADB space plus space Area space of space increment BDC
equals space integral subscript negative 1 end subscript superscript 1 open square brackets fraction numerator 3 straight x plus 7 over denominator 2 end fraction minus fraction numerator straight x plus 5 over denominator 2 end fraction close square brackets dx plus integral subscript 1 superscript 3 open square brackets fraction numerator 11 minus straight x over denominator 2 end fraction minus fraction numerator straight x plus 5 over denominator 2 end fraction close square brackets dx
equals integral subscript negative 1 end subscript superscript 1 open square brackets fraction numerator 2 straight x plus 2 over denominator 2 end fraction close square brackets dx plus integral subscript 1 superscript 3 open square brackets fraction numerator 6 minus 2 straight x over denominator 2 end fraction close square brackets dx
equals integral subscript negative 1 end subscript superscript 1 open square brackets straight x plus 1 close square brackets dx plus integral subscript 1 superscript 3 open square brackets 3 minus straight x close square brackets dx
equals open square brackets straight x squared over 2 plus straight x close square brackets subscript negative 1 end subscript superscript 1 space plus space open square brackets 3 straight x minus straight x squared over 2 close square brackets subscript 1 superscript 3
equals 0 plus 2 plus 9 minus 9 over 2 minus 3 plus 1 half
equals 2 plus 9 over 2 minus 5 over 2
equals 4 space square space units

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Using the method of integration, find the area of the triangular region whose vertices are (2, -2), (4, 3) and (1, 2).



Equation space of space line space AB colon negative
space straight y plus 2 space equals fraction numerator 2 plus 3 over denominator 2 end fraction left parenthesis straight x minus 2 right parenthesis
rightwards double arrow space 2 straight y space equals space 5 straight x minus 14
Equation space of space line space BC colon negative
straight y minus 3 space equals 1 half left parenthesis straight x minus 4 right parenthesis
rightwards double arrow space 3 straight y space equals space straight x plus 5
Equation space of space line space CA colon negative
left parenthesis straight y minus 2 right parenthesis space equals negative 4 left parenthesis straight x minus 1 right parenthesis
4 straight x plus straight y equals 6
therefore space ar space left parenthesis increment ABC right parenthesis
equals integral subscript negative 2 end subscript superscript 3 fraction numerator space 2 straight y space plus 14 over denominator 5 end fraction space dy minus integral subscript 2 superscript 3 3 straight y minus 5 dy space minus integral subscript negative 2 end subscript superscript 2 fraction numerator 6 minus straight y over denominator 4 space end fraction dy
equals 75 over 5 minus 5 over 2 minus 24 over 4
equals fraction numerator 300 minus 120 minus 50 over denominator 20 end fraction space equals space 130 over 20
space equals 13 over 2 space sq. space units
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