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Trigonometry helps you understand any topic that involves distances, angles, or waves. The trig functions (sin, cos, and tan) show up all over science and engineering.

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1. Radians
Discover another way to measure angles.
How to switch back and forth between units for angles
A formula for arc length in terms of radius and angle
Learn what a sector is, and a formula for finding its area
2. Trig functions
Your friendly hypotenuses, opposites, and adjacents
Your very first trig function
Along with sine, cosine is a fundamental trig function
Another important trig function (like sine and cosine)
Find legs of right triangles, and don't get pulled over!
Secant and friends (three more trig functions)
3. Special angles
Calculate the sine, cosine, and tangent of 45 degrees
Calculate the sine, cosine, and tangent of 30 and 60 degrees
Calculate the sine, cosine, and tangent of 0 and 90 degrees
4. The unit circle
What's sin(250)? Use the unit circle to tackle bigger angles
Using the unit circle for trig with negative angles
How trig functions are related for coterminal angles
5. Inverse trig functions
A function that takes you from side ratios to angles
Another inverse trig function
And one last inverse trig function!
6. Trig identities
The tools for simplifying trig expressions
Simplify trig functions of sums
Simplify trig functions of negative angles
Simplify trig functions of differences
Trig functions of twice an angle
Trig functions of three times an angle
Relating squares of trig functions
Trig functions of half an angle
7. Triangle formulas
Relating angles and opposite sides for any triangle
Real-world application of the law of sines to find distances
Relating three sides and an angle for any triangle
Find a triangle's area using 2 sides and the angle between