Answer: True
==================================
Work Shown:
sin(angle) = opposite/hypotenuse
sin(alpha) = MN/NP
sin(alpha) = y/z
---------
cos(angle) = adjacent/hypotenuse
cos(beta) = MN/NP
cos(beta) = y/z
----------
Both sin(alpha) and cos(beta) are equal to y/z, so that means sin(alpha) = cos(beta). This is true because alpha+beta = 90, ie the angles are complementary.
Similarly, you should find that sin(beta) and cos(alpha) are both equal to x/z, which is further proof that the statement is true.