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)
