Every point in the unit circle is identified either by its coordinates
or by the angle it forms with the x-axis,
.
The trigonometric functions associate with every angle
and the correspondant
coordinates the two values

This procedure can be done for every angle
, so you don't have to work with acute angles only.
Would it like.. not be C?? Im guessing its C (:
Answer: 
Step-by-step explanation:
I hope you mean y = x² - 12 and not y = 2x - 12.
You switch the y and x variables:
x = y² - 12
And solve for y:
x + 12 = y²

Answer:
180
Step-by-step explanation:
Subtract the sum of the two angles from 180 degrees.