Let →a,→b be the position vectors of points A and B with respect to O and ∣∣→a∣∣=a,∣∣∣→b∣∣∣=b the points C and D divides A internally and externally in the ratio 2:3 If −−→OC and −−→OD are perpendicular then
A
9a2=4b2
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B
4a2=9b2
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C
9a=4b
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D
4a=9b
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Solution
The correct option is D9a2=4b2 Using section formula,(internally) n→a+m→bm+n −−→OC=3×→a+2×→b5 Using section formula,(externally) n→a−m→bn−m −−→OD=3×→a−2×→b −−→OC⊥ to −−→OD(given) ⇒⎛⎝3×→a+2×→b5⎞⎠(3×→a−2×→b)=0 (3×→a+2×→b)(3×→a−2×→b)=0 9×a2=4×b2 or 9a2=4b2