Work Step by Step
Use the subtraction formula for cosine, $\cos (A+B)=\cos A\cos B-\sin A\sin B$: $\cos(270^\circ+\theta)$ $=\cos 270^\circ\cos \theta-\sin 270^\circ\sin \theta$ $=0*\cos\theta-(-1)*\sin\theta$ $=\sin\theta$
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