pythagorean trigonometric identity造句

I guess cos ( 30?) = sqrt ( 3 ) / 2 is useful too; you can get it from the sine with the Pythagorean trigonometric identity . 90?should also be automatic, as well as 0? just visualize them to figure out where the 0s and 1s go.
It's difficult to find pythagorean trigonometric identity in a sentence. 用pythagorean trigonometric identity造句挺难的