Which of these equations is always true?

sin (x) = cos (x)

sin (x) = cos (90° -

sin (x) = cos (180°

sin (x) = cos (360°-x)

sin (x) = cos (90*-x)

Explanation:

Looking at the graphs of sin (x) and cos (x), you can see that the peaks of the graph are separated by a value of pi/2. If you convert that value into degrees, then the two graphs are separated by 90*. Another way of thinking is from the unit circle. sin (x) = 1 at 90*, and cos (x) = 1 at 0*. The difference is still 90*.