这里需要用到二倍角公式。

Well, you have to use double Angle formulas.

youdao

再次利用二倍角公式。

Well, using, again, the double Angle formula.

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

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