(2∫3sin70°-tan70°)×sin80°怎么解？
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=(3cos20°-cos20°/sin20°)xcos10°
=(3cos20°sin20°-cos20°)xcos10°/
sin20°
=(3/2sin40°-cos20°)/2sin10°
=[3/2(1/2cos10°+√3/2sin10°)-
(√3/2cos10°+1/2sin10°)]/2sin10°
=[3/4cos10°+3√3/4sin10°-√3/2
cos10°-1/2sin10°]/2sin10°
=[(3-2√3)/4cos10°+(3√3-2)/4
sin10°]/2sin10°
=(3-2√3)/8ctg10°+(3√3-2)/8
=(3cos20°sin20°-cos20°)xcos10°/
sin20°
=(3/2sin40°-cos20°)/2sin10°
=[3/2(1/2cos10°+√3/2sin10°)-
(√3/2cos10°+1/2sin10°)]/2sin10°
=[3/4cos10°+3√3/4sin10°-√3/2
cos10°-1/2sin10°]/2sin10°
=[(3-2√3)/4cos10°+(3√3-2)/4
sin10°]/2sin10°
=(3-2√3)/8ctg10°+(3√3-2)/8
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