Let's check:
Let the angle be x
It's complement is 90-x
It's supplement is 180-x
x = 90 - x + 180 - x
x = 270 - 2x
3x = 270
x = 90
So the angle is 90, it's complementary is 0 and it's supplementary is 90... so 90 = 0 + 90
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