原式=1/sin10-√3/cos10=(cos10-√3sin10)/sin10cos10=2(1/2*cos10-√3/2*sin10)/sin10cos10=2(sin30cos10-cos30sin10)/sin10cos10=4sin(30-10)/2sin10cos10=4sin20/sin20=4②cos20°cos40°cos80°=8sin20°cos20°...