作业帮(1/cos280°-3/cos210°)1/cos20°中第4步怎么来的
来源：学生作业帮 编辑：拍题作业网作业帮 分类：数学作业 时间：2024/05/15 00:04:58
(1/cos280°-3/cos210°)1/cos20°中第4步怎么来的
(1/cos^280-3/cos^210)*(1/cos20)
=(1/cos^2(90-10)-3/cos^210)(1/cos20)
=(1/sin^210-3/cos^210)*(1/cos20)
=(cos^210-3sin^210)/(sin^210*cos^210)*(1/cos20)
=(4cos^210-3)/(sin^210*cos^210)*(1/cos20)
=(2cos20-1)/(sin^210*cos^210)*(1/cos20)
=4(2cos20-1)/(sin^210*cos^210)*(1/cos20)
=8 (cos20 - cos60 ) / sin^220 *(1/cos20)
=16sin40sin20 / sin^220 *(1/cos20)
=32 cos20 *(1/cos20)
=32
(1/cos^280-3/cos^210)*(1/cos20)
=(1/cos^2(90-10)-3/cos^210)(1/cos20)
=(1/sin^210-3/cos^210)*(1/cos20)
=(cos^210-3sin^210)/(sin^210*cos^210)*(1/cos20)
=(4cos^210-3)/(sin^210*cos^210)*(1/cos20)
=(2cos20-1)/(sin^210*cos^210)*(1/cos20)
=4(2cos20-1)/(sin^210*cos^210)*(1/cos20)
=8 (cos20 - cos60 ) / sin^220 *(1/cos20)
=16sin40sin20 / sin^220 *(1/cos20)
=32 cos20 *(1/cos20)
=32
因为sin²10°=1-cos²10°
带入第三步就得到第四步
带入第三步就得到第四步
1/cos20°-根号3/sin20°
化简：sin50º(1+√3tan10°)-ｃｏｓ20°/ｃｏｓ８０°√(１-ｃｏｓ２０°)
求sin220°+cos280°+3sin20°cos80°的值．
化简：根号(1-2sin100°cos280°)/{cos370°-根号[1-cos^2(170°)]}
求值:[sin50°(1+tan10°√3)-cos20°]/[cos80°乘以根号下1-cos20°]
求值：【sin50°[1+根号(3)tan10°]—cos20°】/[cos80°根号（1—cos20°）】
化简：【sin50°·（1+√3tan10° ）-cos20°】/（cos80°· √1-cos20°）
化简sin50°（1+√3tan10°）-cos20°/cos80°√（1-cos20°）
锐角三角函数（急）因为cos30°=√3 /2,cos210°= - √3/2,所以cos210°=cos（180°+3
求cos20°cos10
sin40°*(1-sin10°)/[sin10°*(cos20°)^2]
化简：cos20°cos35°1−sin20°