Trigonometry
Determine the exact value of the following trigonometric function without using a calculator.
cos(5π11)cos(6π11)−sin(5π11)sin(6π11)\cos\left(\frac{5\pi}{11}\right)\cos\left(\frac{6\pi}{11}\right)-\sin\left(\frac{5\pi}{11}\right)\sin\left(\frac{6\pi}{11}\right)cos(115π)cos(116π)−sin(115π)sin(116π)
0
1
-1
2