Question

Write the expression as either the sine, cosine, or tangent of a single angle.

Answer 1

the problem resembles that of a cosine of a difference of two angles

Answer 2

\[\cos (A-B)=\cos A \cos B + \sin A \sin B\]

Answer 3

so is it cosin(pi/5 -pi/7)?

Answer 4

@sirm3d?

Answer 5

that's right.

Answer 6

you should combine pi/5-pi/7 into one angle, as required in the problem.

Answer 7

cos π/7?

Answer 8

\[\frac{\pi}{5}-\frac{\pi}{7}=\frac{7\pi-5\pi}{35}=\frac{2\pi}{35}\]