Use a sum or difference identity to find the exact value.
-$\cos ( \theta - \pi )$
A) $\sin \theta$
B) $\cos \theta$
C) $- \cos \theta$
D) $- \sin \theta$

Question

Quizplus · Accepted Answer

The sum or difference identity for cosine is $\cos(\alpha - \beta) = \cos \alpha \cos \beta + \sin \alpha \sin \beta$. Applying this to $\cos(\theta - \pi)$, we get $\cos \theta \cos \pi + \sin \theta \sin \pi$. Since $\cos \pi = -1$ and $\sin \pi = 0$, the expression simplifies to $-\cos \theta$.

Use a Sum or Difference Identity to Find the Exact cos⁡(θ−π)\cos ( \theta - \pi )cos(θ−π)

Use a Sum or Difference Identity to Find the Exact $\cos ( \theta - \pi )$