三角函数的定义是解三角形的基础和依据，教材中首先给出了三角函数的一般定义，即：在直角坐标系中，P（x，y）为角a终边上任意一点，OP一厂，于是可得四个比值，我们把l叫做角。的正弦，记作引n。，即Stn。。上；HDtl做角。的正切，记作ig。，即tga一二；三叫做角。的余切， The definition of the trigonometric function is the basis and basis for solving the triangle. In the textbook, the general definition of the trigonometric function is first given. That is, in the Cartesian coordinate system, P(x, y) is any point on the end of the angle a, OP. , so you get four ratios, we call l the angle. The sine is denoted by n. Stn. . On; HDtl do corner. The tangent is recorded as ig. That is, tga one or two; three are called corners. The rest of the cut,