Let  Find scalars a and b such that  from Mathematics Vector

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 Multiple Choice QuestionsShort Answer Type

21. The position vectors of points A. B, C. D) are straight a with rightwards arrow on top comma space space straight b with rightwards arrow on top comma space space 2 space straight a with rightwards arrow on top space plus space 3 space straight b with rightwards arrow on top  and  straight a with rightwards arrow on top space minus space 2 space straight b with rightwards arrow on top respectively, show that AC with rightwards arrow on top space equals space straight a with rightwards arrow on top space plus space 3 space straight b with rightwards arrow on top space and space DB with rightwards arrow on top space equals space 3 space straight b with rightwards arrow on top space minus space straight a with rightwards arrow on top
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22. Vectors drawn from the origin to the points A, B and C are respectively straight a with rightwards arrow on top. space straight b with rightwards arrow on top space and space 4 space straight a with rightwards arrow on top space space minus space 3 space straight b with rightwards arrow on top. Find AC with rightwards arrow on top space and space BC with rightwards arrow on top.
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23. Give a condition that the three vectors straight a with rightwards arrow on top comma space straight b with rightwards arrow on top space and space straight c with rightwards arrow on top form the three sides of a triangle. What are the other possibilities?
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 Multiple Choice QuestionsLong Answer Type

24. ABCD is a parallelogram. If AB with rightwards arrow on top space equals space straight a with rightwards arrow on top comma space space space BC with rightwards arrow on top space equals space straight b with rightwards arrow on top comma space   then
(i)    Show that AC with rightwards arrow on top space equals straight a with rightwards arrow on top space plus space straight b with rightwards arrow on top comma space space space space BD with rightwards arrow on top space equals space straight b with rightwards arrow on top space minus space straight a with rightwards arrow on top.
(ii) What is the geometrical significance of the relation
                      open vertical bar straight a with rightwards arrow on top space plus space straight b with rightwards arrow on top close vertical bar space equals space open vertical bar straight a with rightwards arrow on top space minus space straight b with rightwards arrow on top close vertical bar ?

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 Multiple Choice QuestionsShort Answer Type

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25.

Let straight u with rightwards arrow on top space equals space straight i with hat on top space plus space 2 space straight j with hat on top comma space space straight v with rightwards arrow on top space equals space minus 2 space straight i with hat on top space plus space straight j with hat on top space and space straight w with rightwards arrow on top space equals space 4 straight i with hat on top space plus space 3 space straight j with hat on top. Find scalars a and b such that straight w with rightwards arrow on top space equals space straight a straight u with rightwards arrow on top space plus space straight b space straight v with rightwards arrow on top.


Here,    straight u with rightwards arrow on top space equals space straight i with hat on top space plus space 2 space straight j with hat on top comma space space straight v with rightwards arrow on top space equals space minus 2 space straight i with hat on top space plus space straight j with hat on top comma space space straight w with rightwards arrow on top space equals space 4 space straight i with hat on top space plus space 3 space straight j with hat on top
therefore                                       straight w with rightwards arrow on top space equals space straight a straight u with rightwards arrow on top space plus space straight b space straight v with rightwards arrow on top.
rightwards double arrow space space space space space space 4 space straight i with hat on top space plus space 3 space straight j with hat on top space equals space straight a space open parentheses straight i with hat on top space plus space 2 space straight j with hat on top close parentheses space plus space straight b space open parentheses negative 2 space straight i with hat on top space plus space straight j with hat on top close parentheses
rightwards double arrow space space space left parenthesis straight a minus 2 straight b minus 4 right parenthesis space straight i with hat on top space plus space left parenthesis 2 straight a plus straight b minus 3 right parenthesis space straight j with hat on top space equals space 0 with rightwards arrow on top
rightwards double arrow space space space space space space space space space space straight a minus 2 straight b minus 4 space equals space 0 space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space... left parenthesis 1 right parenthesis
rightwards double arrow space space space space space space space space 2 straight a plus straight b minus 3 space equals space 0 space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space... left parenthesis 2 right parenthesis
Solving space left parenthesis 1 right parenthesis space and space left parenthesis 2 right parenthesis comma space we space get
space space space space space space space space space space space space space space space fraction numerator straight a over denominator 6 plus 4 end fraction space equals fraction numerator straight b over denominator negative 8 plus 3 end fraction space equals fraction numerator 1 over denominator 1 plus 4 end fraction
therefore space space space space space space space space straight a over 10 space equals fraction numerator straight b over denominator negative 5 end fraction space equals 1 fifth
therefore space space space space space space space space space straight a space equals space 10 over 5 space equals 2 comma space space space space straight b space equals space fraction numerator negative 5 over denominator 5 end fraction space equals space minus 1 space space

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26. If P1 , P2, P3, P4 are points in a plane or space and O, the origin of vectors, show that P4 coincides with O if an only if 
stack OP subscript 1 with rightwards arrow on top space plus space stack straight P subscript 1 straight P subscript 2 with rightwards arrow on top space plus space stack straight P subscript 2 straight P subscript 3 with rightwards arrow on top space plus space stack straight P subscript 3 straight P subscript 4 with rightwards arrow on top space equals space 0 with rightwards arrow on top.
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27. PQRS is a parallelogram. If straight a with rightwards arrow on top comma space straight b with rightwards arrow on top comma space straight c with rightwards arrow on top are the position vectors of the vertices P, Q and R respectively with reference to the origin of reference O ; find the position vector of S with reference to O.

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28.

If straight a with rightwards arrow on top space and space straight b with rightwards arrow on top are the vectors determined by two adjacent sides of a regular hexagon, find the vectors determined by the other sides taken in order.

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29.

If straight a with rightwards arrow on top comma space straight b with rightwards arrow on top comma space straight c with rightwards arrow on top be the vectors represented by the sides of a triangle, taken in order, then prove that straight a with rightwards arrow on top space plus space straight b with rightwards arrow on top space plus space straight c with rightwards arrow on top space equals space 0 with rightwards arrow on top.

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30.

If AO with rightwards arrow on top space plus space OB with rightwards arrow on top space equals space BO with rightwards arrow on top space plus space OC with rightwards arrow on top comma space then prove that the points A, B and C are collinear.

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