在教学同角三角函数间的关系、诱导公式及两角和与差、倍角、半角、和差化积等内容时都要将三角函数式恒等变形；进一步学习三角方程、复数、二次曲线等内容，也要用到三角函数的恒等变形；在物理等学科解决问题时也经常要用到三角 The trigonometric function must be transformed in the same way in teaching the relationship between the trigonometric function, the induced formula and the two angles and differences, multiple angles, half angles, and differential products; further study of triangular equations, complex numbers, quadratic curves Contents such as trigonometric functions are also used in the same content; triangles are often used to solve problems in physics and other disciplines.