The Pythagorean identity

2 videos
1 skill
Prove the Pythagorean trigonometric identity for all real numbers and use it in order to solve problems.

Proof of the Pythagorean trigonometric identity

VIDEO 6:12 minutes
Sal proves the Pythagorean identity (sinθ)^2+(cosθ)^2=1 for all real numbers.

How to find a trig value of an angle given another trig value of the angle (example)

VIDEO 6:15 minutes
Given that sin(θ)=1/2 and that θ is in the third quadrant, Sal finds tan(θ) using the Pythagorean identity.

Use the Pythagorean identity

PRACTICE PROBLEMS
Given the sine (or cosine) of an angle, find its cosine (or sine) using the Pythagorean identity.