这里需要用到二倍角公式。

Well, you have to use double Angle formulas.

youdao

这里再次用二倍角公式。

I mean, here you just use a double Angle again and then you can get it.

youdao

再次利用二倍角公式。

Well, using, again, the double Angle formula.

youdao

用倍角公式可将该三角函数方程转化成一个四次代数方程，然后用求根公式直接求出解析解。

Double Angle formula can transform the circular function equation to a biquadratic algebraic equation, and the analysis solution can be solved by extract equation directly.

youdao

用倍角公式可将该三角函数方程转化成一个四次代数方程，然后用求根公式直接求出解析解。

Double Angle formula can transform the circular function equation to a biquadratic algebraic equation, and the analysis solution can be solved by extract equation directly.

youdao