linear equation of the second order

• 三角函数

linear equation of the second order的用法和样例：

例句

1. Each kind of wave may use the trigonometric function equation to express.
   各种波形曲线均可以用三角函数方程式来表示。
2. The trigonometric terms should be changed by the substitution of the equations involving the double angles.
   用倍角公式代换三角函数项。