## jkl3inberg Group Title Use a sum or difference formula to find the exact value of the following: sin(5π/7)cos(π/21)-cos(5π/7)sin(π/21) one year ago one year ago

1. cwrw238 Group Title

use the identity sin (a - b) = sin a cos b - cos a sin b

2. jdoe0001 Group Title
3. cwrw238 Group Title

so your expression becomes sin (5pi/7 + pi/21)

4. cwrw238 Group Title

= sin 16pi/21