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锐角三角函数问题,都要将问题“定格”在直角三角形中,利用勾股定理求出(或表示出)未知的边,再利用三角函数的概念求出某个锐角的三角函数值,但一定要注意:1弄清楚这个锐角的对边与邻边;2三角函数值要化简.一、直接求:已知直角三角形任意两边时.例1在△ABC中,∠C=90°,AB=221/2,AC=61/2,求cosB的值.分析要求cosB的值,需要已知∠B的邻边和斜边,根据勾股定理可求出∠B的邻边BC的长.
The problem of acute trigonometric functions must all be solved by using the Pythagorean theorem to find (or represent) unknown edges and then use the concept of trigonometric functions to find the trigonometric value of an acute angle. However, we must pay attention to: 1 to find out the sharp edge of the opposite side and adjacent; 2 trigonometric function value to be simplified. A, direct seeking: known right-angled triangle on either side. Example 1 △ ABC, ∠C = 90 ° , AB = 221/2, AC = 61/2, and find the value of cos B. Analyze the value of cosB, we need to know the adjacent edge and hypotenuse of ∠B. According to Pythagorean theorem, long.