# Trigonometry

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