Vector u can be written in component form by subtracting its initial point from its terminal point:
u = (5, -4) -(15, 22) = <-10, -26>
We are told that v = -2u, so ...
v = -2<-10, -26> = <20, 52>
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Multiplying a vector by -1 reverses its direction; multiplying it by some factor k changes its magnitude by a factor of k. To reverse the direction and double the magnitude, we can multiply u by -2.
