Pre-calculus ! express the complex number in trigonometric form. 3 a. 3(cos 0° + i sin 0°) b. 3(cos 90° + i sin 90°) c. 3(cos 180° + i sin 180°) d. 3(cos 270° + i sin 270°)

We have that

 3 = 3 + 0i > rewrite as 3(1 + 0i) 

So now what we have to do is figure out which of the above expressions has cos a = 1 and sin a = 0. 
cos 0 = 1, and sin 0 = 0, so that's the answer that we want. 

the answer is: 
3 = 3(cos 0 + i sin 0)

The answer is part a: use