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The position vectors of `P and Q` are `5hati+4hatj+ahatk and -hati+2hatj-2hatk`, respectively. If the distance between them is 7, then find the value of `a`. |
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Answer» Given points are `P(5hati+4hatj+ahatk) and Q(-hati+2hatj-2hatk)` Now `" "vec(PQ)= (-hati+2hatj-2hatk)-(5hati+4hatj+ahatk)` `" "=(-6hati-2hatj-(2+a)hatk)` Given `|vec(PQ)|=7` `therefore" "sqrt(36+4+(a+2)^(2))=7` or `" "(a+2)^(2)=9 ` or `" "a+2=pm3` or `" "a=-5, 1`. |
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