# Thread: complex numbers - product of polar forms

1. ## complex numbers - product of polar forms

perform the operation and leave in trigonometric form:

(cos 5°+i sin 5°)(cos 20°+i sin 20°)

2. Originally Posted by kassums17
perform the operation and leave in trigonometric form:
(cos 5°+i sin 5°)(cos 20°+i sin 20°)
At least tell us what you do not understand about this.

3. how do you find the cos of 5 degrees and the cos of 20 degrees?

4. Originally Posted by kassums17
how do you find the cos of 5 degrees and the cos of 20 degrees?
There is no need to bother with that.
What does $\left[ {r(\cos (\phi ) + i\sin (\phi ))} \right]\left[ {s(\cos (\theta ) + i\sin (\theta ))} \right] = ~?$