Question

Find a · b, given a = 12(cos pi/3 + i sin(pi/3)), b = 3 (cos(pi/4)+ i sin(pi/4))

Show 3 decimal places.
Please and thank you!!!

Answer 1

a = 12 (cos(π/3) + i sin(π/3))

b = 3 (cos(π/4) + i sin(π/4))

a • b = 36 (cos(π/3) cos(π/4) + i cos(π/3) sin(π/4) + i cos(π/4) sin(π/3) + i ² sin(π/3) sin(π/4))

… = 36 (cos(π/3 + π/4) + i sin(π/3 + π/4))

… = 36 (cos(7π/12) + i sin(7π/12))

… ≈ -9.32 + i 34.8