# trigonometry question? how does 1-cos^2 theta equal sin^2?

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- Mike GLv 73 years ago
Right triangle with legs x and y with hypotenuse h

By Pythagoras

x^2+y^2 = h^2

(x/h)^2+(y/h)^2 = 1

cos^2(θ)+sin2(θ) = 1

sin^2(θ = 1-cos^2(θ)

- oldschoolLv 73 years ago
Values for sine and cosine come from the "unit circle" or a circle with radius = 1. The sine and cosine values are the projections of that radius on the vertical (sine) and horizontal (cosine) axis for angles 0 - 360°. In other words a right triangle with hypotenuse = 1.

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