(1/cos280°-3/cos210°)1/cos20°中第4步怎么来的
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(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°