Question

Use a sum or difference formula to find the exact value of the following.
sin 25Ï€/21 cos 6Ï€/7 - cos 25Ï€/21 sin 6Ï€/7

Answer 1

could someone please explain?

Answer 2

i think you can use the followingidentity here
sin(A - B) =sinAcosB - cosAsinB

Answer 3

So it would be sin 25 - 6?

Answer 4

No sin(25Pi/21 - 6pi/7)
= sin(25pi/21 - 18pi/21)
can you ccontinue?

Answer 5

Okay I got decimal though

Answer 6

0.018

Answer 7

you need to find the angle in terms of pi


it = sin(7pi/21) = sin(pi/3)

now using a standard triangle you can find the exact value of sin(pi/3)