In a triangle OAB , ∠AOB = 90°. If P and Q are the points of

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 Multiple Choice QuestionsLong Answer Type

231.

Prove, using vectors, that the altitudes of a triangle are concurrent.
OR
Prove that the perpendicular from the vertices to the opposite sides of a triangle are concurrent. 

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232. Show that the diagonals of a rhombus bisect each other at right angles.
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233. In a triangle OAB , ∠AOB = 90°. If P and Q are the points of trisection of AB, prove that OP squared space plus space OQ squared space equals space 5 over 9 AB squared


Take O as origin,  OA with rightwards arrow on top space equals straight a with rightwards arrow on top comma space space OB with rightwards arrow on top space equals space straight b with rightwards arrow on top
because space space space angle AOB space equals space 90 degree space space space space space space space space space space space space because space space OA with rightwards arrow on top. space OB with rightwards arrow on top space equals space 0 space space space space space space space space space space space rightwards double arrow space space space straight a with rightwards arrow on top. space straight b with rightwards arrow on top space equals space 0
Let P divide AB in the ratio 1 : 2
because space straight P. straight V. space of space straight P space equals space fraction numerator 2 straight a with rightwards arrow on top space plus space straight b with rightwards arrow on top over denominator 3 end fraction
Let Q divide AB in the ratio 2 : 1
because space straight P. straight V. space of space straight Q space equals space fraction numerator straight a with rightwards arrow on top space plus space 2 space straight b with rightwards arrow on top over denominator 3 end fraction
L.H.S. = OP squared plus OQ squared space equals space open parentheses fraction numerator 2 space straight a with rightwards arrow on top space plus space straight b with rightwards arrow on top over denominator 3 end fraction close parentheses squared space plus space open parentheses fraction numerator straight a with rightwards arrow on top space plus 2 space straight b with rightwards arrow on top over denominator 3 end fraction close parentheses space equals space 1 over 9 open square brackets left parenthesis 2 space straight a with rightwards arrow on top space plus space straight b with rightwards arrow on top right parenthesis space squared space plus space left parenthesis straight a with rightwards arrow on top space plus space 2 space straight b with rightwards arrow on top right parenthesis squared close square brackets
            equals space 1 over 9 open square brackets 4 straight a with rightwards arrow on top squared space plus space straight b with rightwards arrow on top squared space plus space 4 space straight a with rightwards arrow on top. space straight b with rightwards arrow on top space plus space straight a with rightwards arrow on top squared space plus space 4 space straight b with rightwards arrow on top squared space minus space 4 space straight a with rightwards arrow on top. space straight b with rightwards arrow on top close square brackets
equals space 1 over 9 left parenthesis 5 straight a with rightwards arrow on top squared space plus space 5 straight b with rightwards arrow on top squared right parenthesis 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 space space space space space space space open square brackets because space of space left parenthesis 1 right parenthesis close square brackets
space equals 5 over 9 left parenthesis straight a with rightwards arrow on top squared plus space straight b with rightwards arrow on top squared right parenthesis

R.H.S. = 5 over 9 AB squared space equals space 5 over 9 AB with rightwards arrow on top squared space equals space 5 over 9 left parenthesis straight P. straight V. space of space straight B space minus space straight P. straight V. space of space straight A right parenthesis squared

           equals space 5 over 9 left parenthesis straight b with rightwards arrow on top space minus space straight a with rightwards arrow on top right parenthesis squared space equals space 5 over 9 left square bracket straight b with rightwards arrow on top squared space plus space straight a with rightwards arrow on top squared space minus space space 2 space straight b with rightwards arrow on top. space straight a with rightwards arrow on top right square bracket space equals space 5 over 2 left parenthesis straight a with rightwards arrow on top squared space plus space straight b with rightwards arrow on top squared right parenthesis space space space space left square bracket because space of space left parenthesis 1 right parenthesis right square bracket
because space space space space straight L. straight H. straight S. space equals space straight R. straight H. straight S.

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234. In a tetrahedron, if two pairs of opposite edges are perpendicular, then the third pair is also perpendicular to each other and the sum of the sequares of two opposite edges is the same for each pair.
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235.

Find straight lambda space and space straight mu if  left parenthesis 2 space straight i with hat on top space plus space 6 space straight j with hat on top space plus space 27 space straight k with hat on top right parenthesis space cross times left parenthesis straight i with hat on top space cross times space straight lambda space straight j with hat on top space plus space straight mu space straight k with hat on top right parenthesis space equals space 0 with rightwards arrow on top.

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 Multiple Choice QuestionsShort Answer Type

236.

Find open vertical bar straight a with rightwards arrow on top space cross times space straight b with rightwards arrow on top close vertical bar comma space space space if space space straight a with rightwards arrow on top space equals space 2 space straight i with hat on top space plus straight j with hat on top space plus space 3 straight k with hat on top space and space straight b with rightwards arrow on top space equals space 3 space straight i with hat on top space plus space 5 space straight j with hat on top space minus space 2 space straight k with hat on top.

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237.

Find open vertical bar straight a with rightwards arrow on top space cross times space straight b with rightwards arrow on top close vertical bar  if  straight a with rightwards arrow on top space equals straight i with hat on top space minus space 7 space straight j with hat on top space plus space 7 space straight k with hat on top and straight b with rightwards arrow on top space equals space 3 straight i with hat on top space minus space 2 straight j with hat on top space plus space 2 straight k with hat on top

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238.

If straight a with rightwards arrow on top space equals space straight i with hat on top space plus space straight j with hat on top space minus space 3 space straight k with hat on top space and space straight b with rightwards arrow on top space equals 3 space straight i with hat on top space minus space 2 space straight j with hat on top space plus space 2 space straight k with hat on top comma space space find space open vertical bar 2 straight b with rightwards arrow on top cross times space straight a with rightwards arrow on top close vertical bar.

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 Multiple Choice QuestionsLong Answer Type

239.

If straight a with rightwards arrow on top space equals straight i with hat on top space minus straight j with hat on top space plus space 2 space straight k with hat on top comma space space straight b with rightwards arrow on top space equals space 2 space straight i with hat on top space minus space 3 space straight j with hat on top space minus space 4 space straight k with hat on top comma then show that straight a with rightwards arrow on top space cross times space straight b with rightwards arrow on top space equals space minus straight b with rightwards arrow on top space cross times space straight a with rightwards arrow on top

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 Multiple Choice QuestionsShort Answer Type

240. Find a unit vector perpendicular to both straight a with rightwards arrow on top space and space straight b with rightwards arrow on top if  straight a 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 space plus space 2 space straight k with hat on top space space and space straight b with rightwards arrow on top space equals space 2 space straight i with hat on top space plus space 5 space straight j with hat on top space minus space 3 space straight k with hat on top

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