Answer
$90^\circ$.
Work Step by Step
From what we learned: $\cos\theta=\frac{U\cdot V}{|U||V|}=\frac{0\cdot(-4)+17\cdot0}{\sqrt{0^2+(-4)^2}\sqrt{17^2+0^2}}=\frac{0}{4\cdot17}=0$
Thus $\theta=\cos^{-1}0=90^\circ$.
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