Determine the values of x for which the function  is increasin

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 Multiple Choice QuestionsLong Answer Type

161.

Prove that straight y equals space fraction numerator 4 space sin space straight theta over denominator 2 plus cos space straight theta end fraction minus straight theta is an increasing function of straight theta in open square brackets 0 comma space straight pi over 2 close square brackets.

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162.

Find the intervals in which the function f is given by
                         straight f left parenthesis straight x right parenthesis space equals space fraction numerator 4 space sin space straight x space minus space 2 straight x minus space straight x space cosx over denominator 2 plus cos space straight x end fraction
is (i) increasing    (ii)  decreasing

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163.

Determine the values of x for which the function straight f left parenthesis straight x right parenthesis space equals fraction numerator straight x over denominator straight x squared plus 1 end fraction is increasing and for which it is decreasing.


Here straight f left parenthesis straight x right parenthesis space equals fraction numerator straight x over denominator straight x squared plus 1 end fraction
therefore space space space straight f apostrophe left parenthesis straight x right parenthesis space equals fraction numerator left parenthesis straight x squared plus 1 right parenthesis. space 1 minus straight x. space 2 straight x over denominator left parenthesis straight x squared plus 1 right parenthesis squared end fraction space equals space fraction numerator 1 minus straight x squared over denominator left parenthesis straight x squared plus 1 right parenthesis squared end fraction
For straight f left parenthesis straight x right parenthesis to be increasing,  straight f apostrophe left parenthesis straight x right parenthesis space greater than space 0
therefore space space space space space fraction numerator 1 minus straight x squared over denominator left parenthesis straight x squared plus 1 right parenthesis squared end fraction greater than 0 space space space space space rightwards double arrow space space 1 minus straight x squared greater than 0 space space space space space rightwards double arrow space space space 1 greater than straight x squared
rightwards double arrow space space space space space straight x less than 1 space space space space space space space space space space space space space space space space space space rightwards double arrow space space space space open vertical bar straight x squared close vertical bar space less than space space 1 space space space space space space space space rightwards double arrow space space space space open vertical bar straight x close vertical bar space less than space 1
rightwards double arrow space space space space space 1 space less than space straight x space space less than space 1
therefore space space space space straight f left parenthesis straight x right parenthesis space is space increasing space for space minus 1 less than straight x less than 1
therefore space space space space straight f left parenthesis straight x right parenthesis space is space increasing space when space straight x space element of space left parenthesis negative 1 comma space 1 right parenthesis
Again space straight f left parenthesis straight x right parenthesis space is space decreasing space when space straight f apostrophe left parenthesis straight x right parenthesis space less than space 0
space therefore space space space space space fraction numerator 1 minus straight x squared over denominator left parenthesis straight x squared plus 1 right parenthesis squared end fraction less than 0 space space space space space space space space rightwards double arrow space space space space space space 1 minus straight x squared less than 0 space space space space space space space space space rightwards double arrow space space space space 1 less than straight x squared
rightwards double arrow space space space space straight x squared greater than 1 space space space space space rightwards double arrow space space space space straight x squared greater than 1 space space space space space space space rightwards double arrow space space space space open vertical bar straight x close vertical bar squared greater than 1 space space space space space space space rightwards double arrow space space space space space open vertical bar straight x close vertical bar greater than 1
rightwards double arrow space space space either space straight x less than negative 1 space space space space space or space space space space space straight x greater than 1
therefore space space space space space straight f left parenthesis straight x right parenthesis space is space decreasing space for space straight x less than negative 1 space space space space or space space space space space straight x greater than 1
therefore space space space space straight f left parenthesis straight x right parenthesis space is space decreasing space when space straight x comma space element of space space space space left parenthesis negative infinity comma space space minus 1 right parenthesis space union space space space space space left parenthesis 1 comma space space space infinity right parenthesis

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 Multiple Choice QuestionsShort Answer Type

164. Prove that the function x2 – x + 1 is neither increasing nor decreasing on (0, 1).
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165.

Let I be any interval disjoint from (– 1, 1). Prove that the function f given by straight f apostrophe left parenthesis straight x right parenthesis space equals space straight x plus 1 over straight x is strictly increasing on I.

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166.

Find the intervals in which the following function is decreasing:
f (x) = x– 12x

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167.

Find the intervals in which the function f given by f(x) = 2x2 – 3x is
(a) strictly increasing    (b) strictly decreasing

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168.

Find the intervals in which the function f given by f(x) = x2 – 4x+6  is
(a) strictly increasing    (b) strictly decreasing

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169.

Find the intervals in which the following functions are strictly increasing or decreasing:
x2+ 2x – 5

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170.

Find the intervals in which the following functions are strictly increasing or decreasing:
10 – 6x – 2x2

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