trigonometrical substitution

例句：

1. 1.The trigonometrical substitution method is used to solve problems involving angles.
   三角学替换方法用于解决涉及角度的问题。
2. 2.In this study, we use the trigonometrical substitution to find the area of a circle.
   在这项研究中，我们使用三角学替换来找到圆的面积。
3. 3.The trigonometrical substitution was introduced by Euler in his work on the theory of curves.
   三角学替换是由欧拉在他的曲线理论工作中引入的。