The position vectors of points A,B,C and D are A=3^i+4^j+5^k,B=4^i+5^j+6^k, C=7^i+9^j+3^k and D=4^i+6^j. Then, the displacement vectors AB and CD are
A
perpendicular
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B
parallel
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C
antiparallel
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D
inclined at an angle of 60∘
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Solution
The correct option is C antiparallel We know, −−→AB=→B−→A −−→AB=(4^i+5^j+6^k)−(3^i+4^j+5^k) −−→AB=^i+^j+^k Similarly, −−→CD=→D−→C −−→CD=(4^i+6^j)−(7^i+9^j+3^k) −−→CD=−3^i−3^j−3^k
So we can write, −−→CD=−3(−−→AB). ∴ Vectors AB and CD are antiparallel