问题
解答题
深化拓展：求cot10°-4cos10°的值．
答案
提示：cot10°-4cos10°
=
-4cos10°cos10° sin10°
=cos10°-2sin20° sin10°
=cos(30°-20°)-2sin20° sin10°
=
cos20°+3 2
sin20°-2sin20°1 2 sin10°
=
cos20°-3 2
sin20°3 2 sin10°
=
sin(30°-20°)3 sin10°
=3
故答案：3