Answer
$\frac{3\pi}{4},\frac{7\pi}{4}$
Work Step by Step
1. $cos\theta-sin(-\theta)=0 \Longrightarrow cos\theta+sin\theta=0 \Longrightarrow tan\theta=-1 $,
2. $tan\theta=-1 \Longrightarrow \theta=\frac{3\pi}{4},\frac{7\pi}{4}$ in $[0,2\pi)$.
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