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The Pythagorean identity
Prove the Pythagorean trigonometric identity for all real numbers and use it in order to solve problems.
Sal proves the Pythagorean identity (sinθ)^2+(cosθ)^2=1 for all real numbers.
Given that sin(θ)=1/2 and that θ is in the third quadrant, Sal finds tan(θ) using the Pythagorean identity.
Given the sine (or cosine) of an angle, find its cosine (or sine) using the Pythagorean identity.