## Trigonometry (11th Edition) Clone

Angle $(A+B)$ lies in quadrant III.
Take a look back the results in 2 previous parts: $$\sin(A+B)=-\frac{63}{65}$$ and $$\cos(A+B)=-\frac{16}{65}$$ Both $\sin(A+B)$ and $\cos(A+B)$ are negative, so angle $(A+B)$ must lie in quadrant III.