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*.