So if the point P ( − 45 , y ) is on the unit circle in quadrant II, then what is y=?

Answer 1

I'm guessing the problem is supposed to have the point P at (-4/5, y) since the radius of the "unit circle" is 1 unit making and x-value of -45 impossible.

Here is a sketch:

Can you see that a triangle is formed with the hypotenuse equal to 1 and the bottom leg equal to 4/5 (you can ignore the negative for the moment)? Doesn't the Pythagorean Theorem seem useful to you to find the other leg?