Question

求值,sin10度乘sin50度乘sin70度是多少？ 答案是1/8 为什么？ 谢谢

Answer 1

sin10°Xsin50°Xsin70°=sin(90°-80°)sin(90°-40°)sin(90°-20°)
=cos20°Xcos40°Xcos80°
=sin20°Xcos20°Xcos40°Xcos80°/sin20°
=1/2Xsin40°Xcos40°Xcos80°/sin20°
=1/8Xsin160°/sin20° sin160°=sin20°
=1/8

Answer 2

你好，解答如下：
sin10°sin50°sin70°
=sin10°sin50°cos20°
=sin10°sin50°cos20°cos10°/cos10°
=1/2sin20°cos20°sin50°/cos10°
=1/4sin40°cod40°/sin80°
=1/8sin80°/sin80°
=1/8