# Trigonometry with right triangles

Contents

Meet your new best friends: sine, cosine, and tangent.

Learn how to find a side length in a right triangle when given one side length and one acute angle.

Learn how to find an acute angle in a right triangle when given two side lengths.

Solve real-world problems that can be modeled by right triangles, using trigonometry.

Learn how the trigonometric ratios are derived from triangle similarity considerations.

Learn about the relationship between the sine of an angle and the cosine of its complementary angle, which is the angle that completes to 90°.

Learn to find the sine, cosine, and tangent of 45-45-90 triangles and also 30-60-90 triangles.

Learn about a very special trigonometric identity that follows from the Pythagorean theorem.

Learn about the remaining three side ratios in a right triangle: the secant, the cosecant, and the cotangent.