Trigonometry: Math Terms Explained
Plain-language definitions of every trigonometry term your child meets in school, each with kid-friendly explanations, worked examples, and common mistakes to watch for.
Amplitude
Amplitude is the distance from the midline of a sinusoidal graph (like sine or cosine) to its highest or lowest point, and it measures how far the graph swings above and below the midline.
Cosine
Cosine is a trigonometric ratio that compares the length of the adjacent side to the hypotenuse in a right triangle, and for any angle on the unit circle it is the x-coordinate of the point on the circle.
Inverse trigonometric functions
Inverse trigonometric functions are functions that undo the basic trigonometric functions, taking a ratio like sine, cosine, or tangent and giving back the angle that produced it.
Law of cosines
The law of cosines is a formula that relates the lengths of the three sides of any triangle to the cosine of one of its angles, and it lets you find a missing side or angle when the triangle is not a right triangle.
Law of sines
The law of sines is a trigonometry rule that relates the side lengths of a triangle to the sines of its angles: in any triangle, a/sin(A) = b/sin(B) = c/sin(C).
Period
A period in math is the horizontal length of one complete repeating cycle of a graph or pattern, such as a sine or cosine wave, before it starts to repeat again.
Radian
A radian is a way to measure angles using the radius of a circle, defined as the ratio of an arc's length to the circle's radius, so it has no units like degrees do.
Sine
Sine is a trigonometric ratio that compares the length of the side opposite an angle to the length of the hypotenuse in a right triangle, and it can also be defined using coordinates of points on the unit circle.
Tangent
A tangent is a line or segment that touches a circle at exactly one point, and in trigonometry, tangent is a ratio that compares the opposite side of a right triangle to the adjacent side for a given angle.
Trigonometric identity
A trigonometric identity is an equation involving trigonometric functions, such as sine, cosine, and tangent, that is true for every value of the variable where both sides are defined.
Trigonometric ratios
Trigonometric ratios are functions that relate an angle in a right triangle to the ratios of that triangle's side lengths, and they are also defined using coordinates on the unit circle.
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