Show that cos(pi - θ) = -cos θ
for every angle θ
Use the identity
cos(a - b) = cos a cos b + sin a sin b
In your case, a = pi, and b = è. Remember that sin pi = 0 and cos pi = -1
for every angle θ
cos(a - b) = cos a cos b + sin a sin b
In your case, a = pi, and b = è. Remember that sin pi = 0 and cos pi = -1