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# FP4 Vector Question

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1. Hey, does anybody know how to answer this question... the point A is (2, 9, t) and B is (2t, 5, 3t), first find the modulus (magnitude) of vector A to B, then give the value of t that would make this modulus minimum, then state the value of this minimum. The answer says the value of t= 0.5 and the value of the minimum is 3 root 2 but I have no idea where this comes from????
2. (Original post by hep12345)
Hey, does anybody know how to answer this question... the point A is (2, 9, t) and B is (2t, 5, 3t), first find the modulus (magnitude) of vector A to B, then give the value of t that would make this modulus minimum, then state the value of this minimum. The answer says the value of t= 0.5 and the value of the minimum is 3 root 2 but I have no idea where this comes from????
You have a quadratic (I think) function of t inside the square root, find the minimum of that using completing the square/differentiation/whatever.

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