ACT Preparation / Unit 14 ACT 1327 short lesson, about 20 seconds
The Pythagorean Identity
Captions available
The idea
For every angle, sin²θ + cos²θ = 1, because the point (cos θ, sin θ) lies on the unit circle.
In practice
If sin θ = 0.6, then cos²θ = 1 − 0.36 = 0.64, so cos θ = ±0.8.
Where people slip
The quadrant decides the sign of the root. And sin²θ means (sin θ)², the sine squared, not the sine of θ².
Your place on the trail
Every lesson rests on earlier ones and opens later ones. Tap any to jump.
Builds on
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