Which property can be justified using the ratios in triangle xyz ?
a) cos y = xz
b) sin y = cos (90o - y)
c) cos z = sin (90o - y)
d) tan z = cos ysin z

The correct answer is B.

Determine and recall first the trigonometric functions:

Sin A = Opposite/Hypotenuse
Cos A = Adjacent/Hypotenuse
Tangent = Opposite/Adjacent

If for example we try to take an angle, for example the Y, then Y is opposite Y. The Hypotenuse will be the longer side which is going to denoted by X and the next side will be Adjacent which will be denoted by Z. 

Use this test to

Sin Y = Y/X

where:

Y = opposite
X = hypotenuse 

Cos (90 - y) = cos (90 - 50) = cos 40

where Z = 40
we look for cos Z = Y/X

Therefore,

Sin Y = Cos (90 - Y)