第1个回答 2013-01-03
分子和分母同时乘以 cos10°
sin10°×sin50°×sin70°
= sin10°×sin50°×sin70°× cos10°/cos10°
= (1/2) × sin20°× sin50°× sin70°/cos10°
= (1/2) × sin20°× sin50°× cos20°/cos10°
= (1/4) × sin40°× sin50°/cos10°
= (1/4) × sin40°× cos40°/cos10°
= (1/8) × sin80°/cos10°
= (1/8) × sin80°/sin80°
= 1/8来自:求助得到的回答