Sin 正弦，cos 余弦，tan 正切，是三個(gè)最常用的三角函數(shù)。

The simplest definitions of the trigonometrical functions are given in terms of the ratios of the sides of a right-angled triangle, for values of the angle θ between 0° and 90°.

首先，通過直角三角形，在0到90度范圍內(nèi)來討論最基礎(chǔ)的三角函數(shù)。

Evaluating Trigonometric Functions

Use the triangle to find the values of .

Solution:

By the Pythagorean Theorem,

(hyp)2?= (opp)2?+ (adj)2, it follows that

Find the three trigonometric ratios ?of ?the angles 30°and 60°

Find the three trigonometric ratios of the angle 45°

The triangle PQR is a right-angled isosceles triangle with equal sides of length 1 unit.

Trigonometric function of special angles

特殊角的三角函數(shù)值