求(1+cos20°)/cos10°-sin10°(1/tan5°-tan5°)的值
问题描述：
求(1+cos20°)/cos10°-sin10°(1/tan5°-tan5°)的值
答
(1+cos20°)/cos10°-sin10°(1/tan5°-tan5°)
=(1+2cos^2(10)-1)/cos10-sin10[cos5/sin5-sin5/cos5]
=2cos10-sin10(cos^2(5)-sin^2(5))/(sin5cos5)
=2cos10-sin10(cos10/(1/2sin10)
=2cos10-2cos10
=0