## anonymous one year ago Find the product of the complex numbers. Express your answer in trigonometric form. z1=3(cos(pi/4)+i sin(pi/4)) z2=7(cos(3pi/8)+i sin(3pi/8))

1. tkhunny

2. anonymous

so 3*7?

3. tkhunny

Now, the second part.

4. anonymous

multiply pi/4*pi/4?

5. tkhunny

6. anonymous

7. tkhunny

Why would you do that? When you came up with 3*7, you took a value from each of z1 and z2. You should do the same with the addition.

8. anonymous

you add 3 and 7? is that what you're saying?

9. tkhunny

No, Please don't reverse correct things you did already. Multiply the leading constants: 3*7 -- Done. Don't change that. Add the angles: ?? + ??

10. anonymous

ok I think I understand I use the unit circle to figure out the angle then I add?

11. tkhunny

?? The angles are given. Why do you need a unit circle? $$\dfrac{\pi}{4}+\dfrac{3\pi}{8}$$ -- Go!

12. anonymous

5pi/8

13. tkhunny

Now, if this happens to be greater than $$2\pi$$, you might need that Unit Circle. What is your final answer? You have all the pieces.

14. anonymous

So do I do 21cos(5pi/8)+i sin(5pi/8) ?

15. tkhunny

Not quite. The parentheses are not optional.

16. anonymous

21(cos(5pi/8)+i sin(5pi/8))

17. tkhunny

Perfect.

18. anonymous

okay let me solve

19. tkhunny

Solve what? You are done. Move on to the next one.

20. anonymous

oh that's it?

21. tkhunny

That's all there is to it. :-)

22. anonymous

thanks

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