If  and , show that(i)  have the same direction and (ii) 

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 Multiple Choice QuestionsLong Answer Type

41. ABCD is a quadrilateral and O is any point in its plane. Show that it OA with rightwards arrow on top space plus space OB with rightwards arrow on top space plus space OC with rightwards arrow on top space plus space OD with rightwards arrow on top space equals space 0 with rightwards arrow on top then O is the point of intersection of lines joining the middle points of the opposite sides of ABCD.
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42. For any two vectors straight a with rightwards arrow on top space and space straight b with rightwards arrow on top, prove that
(i)        open vertical bar straight a with rightwards arrow on top space plus space straight b with rightwards arrow on top close vertical bar space less or equal than space open vertical bar straight a with rightwards arrow on top close vertical bar space plus space open vertical bar straight b with rightwards arrow on top close vertical bar              (ii)     open vertical bar straight a with rightwards arrow on top space minus space straight b with rightwards arrow on top close vertical bar space less or equal than space open vertical bar straight a with rightwards arrow on top close vertical bar space plus space open vertical bar straight b with rightwards arrow on top close vertical bar         (iii) open vertical bar straight a with rightwards arrow on top space minus space straight b with rightwards arrow on top close vertical bar space space space greater-than or slanted equal to space space open vertical bar straight a with rightwards arrow on top close vertical bar space minus space open vertical bar straight b with rightwards arrow on top close vertical bar

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43.

If straight c with rightwards arrow on top space equals space 3 straight a with rightwards arrow on top space plus space 4 straight b with rightwards arrow on top and 2 straight c with rightwards arrow on top space equals space straight a with rightwards arrow on top space minus space 3 straight b with rightwards arrow on top, show that
(i) straight c with rightwards arrow on top space and space straight a with rightwards arrow on top have the same direction and open vertical bar straight c with rightwards arrow on top close vertical bar space greater than space open vertical bar straight a with rightwards arrow on top close vertical bar
(ii) straight c with rightwards arrow on top space and space straight b with rightwards arrow on top have opposite direction and 


Here straight c with rightwards arrow on top space equals space 3 space straight a with rightwards arrow on top space plus space 4 space straight b with rightwards arrow on top and 2 space straight c with rightwards arrow on top space equals space straight a with rightwards arrow on top space minus space 3 space straight b with rightwards arrow on top
therefore space space space 2 space left parenthesis 3 space straight a with rightwards arrow on top space plus space 4 space straight b with rightwards arrow on top right parenthesis space equals space straight a with rightwards arrow on top minus space 3 space straight b with rightwards arrow on top space space space space rightwards double arrow space space space 6 space straight a with rightwards arrow on top space plus space 8 space straight b with rightwards arrow on top space equals space straight a with rightwards arrow on top space minus space 3 space straight b with rightwards arrow on top
rightwards double arrow space space space 5 space straight a with rightwards arrow on top space equals space minus 11 space straight b with rightwards arrow on top
therefore space space space space straight a with rightwards arrow on top space equals space minus 11 over 5 straight b with rightwards arrow on top space and space straight b with rightwards arrow on top space equals space minus 5 over 11 straight a with rightwards arrow on top space space space space space space space space space space space space space space space space space space... left parenthesis 1 right parenthesis
(i)    straight c with rightwards arrow on top space equals space 3 space straight a with rightwards arrow on top space plus space 4 space straight b with rightwards arrow on top space equals space 3 space straight a with rightwards arrow on top space plus space 4 space open parentheses negative 5 over 11 straight a with rightwards arrow on top close parentheses                             open square brackets because space space of space left parenthesis 1 right parenthesis close square brackets
           equals space 3 space straight a with rightwards arrow on top space minus space 20 over 11 space straight a with rightwards arrow on top space equals space 13 over 11 straight a with rightwards arrow on top


Also,     open vertical bar straight c with rightwards arrow on top close vertical bar space equals space 13 over 11 open vertical bar straight a with rightwards arrow on top close vertical bar space space space space rightwards double arrow space space space space space space space open vertical bar straight c with rightwards arrow on top close vertical bar space greater than space open vertical bar straight a with rightwards arrow on top close vertical bar.
(ii) straight c with rightwards arrow on top space equals space 3 space straight a with rightwards arrow on top space plus space 4 space straight b with rightwards arrow on top space equals space 3 space open parentheses negative 11 over 5 straight b with rightwards arrow on top close parentheses space plus space 4 space straight b with rightwards arrow on top                     open square brackets because space space of space left parenthesis 1 right parenthesis close square brackets
       equals space minus 33 over 5 straight b with rightwards arrow on top space plus space 4 space straight b with rightwards arrow on top space equals space minus 13 over 5 straight b with rightwards arrow on top

therefore space space space straight c with rightwards arrow on top space and space straight b with rightwards arrow on top space have space opposite space directions. space
Also,                open vertical bar straight c with rightwards arrow on top close vertical bar space equals space 13 over 5 open vertical bar straight b with rightwards arrow on top close vertical bar space space space space space space space space space space rightwards double arrow space space space space space space space open vertical bar straight c with rightwards arrow on top close vertical bar space greater than space open vertical bar straight b with rightwards arrow on top close vertical bar.

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 Multiple Choice QuestionsShort Answer Type

44. Show that the line joining the middle points of the consecutive sides of a quadrilateral is a parallelogram.
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 Multiple Choice QuestionsLong Answer Type

45. In the figure, M is the mid-point of AB and N is the mid-point of CD and O is the mid-point of MN. Prove that
(i) OA with rightwards arrow on top space plus space OB with rightwards arrow on top space plus space OC with rightwards arrow on top space plus space OD with rightwards arrow on top space equals space straight O with rightwards arrow on top
(ii) BC with rightwards arrow on top space plus space AD with rightwards arrow on top space equals space 2 space MN with rightwards arrow on top

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46. Prove by vector method that the line segment joining the mid-points of the diagonals of trapezium is parallel to the parallel sides and equal to help of there difference.
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47. ABCD is a parallelogram. If L and M are the mid-point of BC and DC respectively, then express AL with rightwards arrow on top space and space AM with rightwards arrow on top in terms of AB with rightwards arrow on top space and space AD with rightwards arrow on top.
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48. ABCDEF is a regular hexagon. Show that
(i)  AB with rightwards arrow on top space plus space AC with rightwards arrow on top space plus space AD with rightwards arrow on top space plus space AE with rightwards arrow on top space plus space AF with rightwards arrow on top space equals space 3 space AD with rightwards arrow on top
(ii) AB with rightwards arrow on top space plus space AC with rightwards arrow on top space plus space AD with rightwards arrow on top space plus space AE with rightwards arrow on top space plus space AF with rightwards arrow on top space equals space 6 space AO with rightwards arrow on top
where O is centre of the hexagon.
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49. Prove that the sum of all the v ectors from the centre of a regular octagon to its vertices is the zero vector.
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50. Show that the sum of three vector determined by the medians of a triangle directed from the vertices is zero.
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