why is cos(90)=0?

why is cos(90)=0? (degrees)

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Think about this.....on a unit circle, the "x" value at pi/2 (90 degrees)  = 0 and the value of "r" always = 1.

Since the cos(θ) = x / r      then cos(90) = 0 / 1   =  0

Also, look at the cosine graph......notice at pi/2 that the curve crosses the x axis at that point, i.e., the value of the cosine at that point = 0