For the last section of my Trig class (Math 1060), we're working with graphing complex #s. I'm able to do most questions correctly, but there have been a few where I can't get the right answer and I don't know what I'm doing wrong. Here's one of those questions:
Find the trigonometric form of the number:
-7 + 4i
Now, here's what I've done so far. To find r, I took the square root of (-7)^2 + (4)^2. This equals sqrt(65). That part I've done right, according to the back of the book.
Now onto finding the sin and cos. For every other problem, I've taken the tangent of theta, which is (b/a). So, that would be (-4/7). The arctan of that is -29.74. . . but the back of the book says the angle should be 2.62.
I know once I find the angle the answer will look like sqrt(65)(cos (angle), i sin(angle)), but I can't get the angle! What am I doing wrong?