根号[(3/sin20')-(1/cos20')],
问题描述：
根号[(3/sin20')-(1/cos20')],
答
√3/sin20°-1/cos20°
=(√3cos20°-sin20°)/sin20°cos20°
=2(sin60°cos20°-cos60°sin20°)/sin20°cos20°
=2sin40°/0.5sin40°=4.