Question

Use an Addition or Subtraction Formula to write the expression as a trigonometric function of one number. sin 3π /7 cos 2π/ 21 − cos 3π/ 7 sin 2π/ 21

Answer 1

Answer:

sin(3π/7 - 2π/21)

Step-by-step explanation:

Given

sin 3π /7 cos 2π/ 21 − cos 3π/ 7 sin 2π/ 21

Required

Write a trigonometry formula for the expression

Using sine formula, we have:

sin(A - B) = sinAcosB - cosAsinB

The above formula can be applied to the given expression where

A = 3π/7

B = 2π/21

So, the trigonometry formula is:

sin 3π /7 cos 2π/ 21 − cos 3π/ 7 sin 2π/ 21= sin(3π/7 - 2π/21)