Trigonometry is greek for triangle measurement.
Three of the most basic ideas in trigonometry are the sine, cosine, and tangent ratios. The sine, cosine, and tangent ratios can be defined as follows.
I have attached right triangle ABC in the image attached.
In right triangle ABC, the sine of angle A is equal to the ratio of the length of the side opposite angle A to the length of the hypotenuse. So in right triangle ABC, the sine of angle A equals y over z. The abbreviation we use for sine is sin.
Next, the cosine of angle A is equal to the ratio of the length of the side adjacent to angle A to the length of the hypotenuse. So in right triangle ABC, the cosine of angle A equals x over z. The abbreviation we use for cosine is cos.
Finally, the tangent of angle A is equal to the ratio of the length of the side opposite angle A to the length of the side adjacent to angle A. So in right triangle ABC, the tangent of angle A equals y over x. The abbreviation we use for tangent is tan.
An easy way to remember the sine, cosine, and tangent ratios is to use the word SOH-CAH-TOA.
Sine is opposite over hypotenuse, cosine is adjacent over hypotenuse, and tangent is opposite over adjacent.
