sin70°等于多少

sin10°sin30°sin50°sin70°=(1/2)sin10°sin50°sin70°=(1/2)cos80°cos40°cos20°=(1/2)cos80°cos40°cos20°sin2

[cos40°+sin50°(1+√3tan10°)]/[sin70°√(1+cos40°)]=[cos40°+sin50°×（tan60°-tan10°）/tan50°]/sin70°(√2)cos

上下乘√2/2原式=(sin70*√2/2-cos70*√2/2)/(sin70*√2/2+cos70*√2/2)=(sin70cos45-cos70sin45)/(sin70cos45+cos70s

[cos40°+sin50°(1+√3tan10°)]/[sin70°√(1+cos40°)]=[cos40°+sin50°×（tan60°-tan10°）/tan50°]/sin70°(√2)cos

分子分母同时乘以cos10°sin10°×sin50°×sin70°=sin10°×sin50°×sin70°×cos10°/cos10°=sin10°×cos10°×sin50°×sin70°/co

换成cos变成：cos80＊cos40＊cos20乘上sin20,倍角公式,变成sin160／（sin20＊8）＝1／8

sin10°sin50°sin70°=1/2(2cos10°sin10°sin50°sin70°）/cos10°=1/2(sin20°cos20°sin50°）/cos10°=1/4(sin40°co

题目错了吧sin80应该是sin30sin10sin30sin50sin70=cos10sin10sin30sin50sin70/cos10=1/2sin20sin70sin30sin50/cos10

sin10°*sin50°*sin70°=0.17*0.77*0.94=0.12

(2cos10°-sin20°)/sin70°=(2cos10°-sin20°)/cos20°=[cos10°+(cos10°-cos70°)]/cos20°=[cos10°+2sin40°*sin3

cos40°+sin50°×（1+√3tan10°）=cos40°+sin50°×（tan60°-tan10°）/tan50°=cos40°+（tan60°-tan10°）cos50°=cos40°+

sin10*sin50*sin70=cos20cos40cos80=sin20cos20cos40cos80/sin20=1/2sin40cos40cos80/sin20=1/4sin80cos80/

(3-sin70°)/(2-cos²10°)=(3-cos20°)/[2-(1+cos20°)/2]=2(3-cos20°)/(4-1-cos20°)=2(3-cos20°)/(3-cos2

sin10°×sin50°×sin70°=sin10°×sin50°×sin70°×cos10°/cos10°=sin10°×cos10°×sin50°×sin70°/cos10°=(1/2)×sin

=sin10sin50-sin70sin10-sin50sin70=sin10{sin(60-10)-sin(60+10)}-sin(60-10)sin(60+10)=sin10(-2sin10*co

sin10*sin50*sin70=cos80*cos40*(cos20*sin20)/sin20=cos80*(cos40*sin40)/(2sin20)=cos80*sin80/(4sin20)=

cos40°+sin50°(1+3tan10°)sin70°1+sin50°=cos40°+sin50°(1+3sin10°cos10°)cos20°1+cos40°==cos40°+cos40°(2

sin70°sin65°-sin20°sin25°=cos20°sin65°-sin20°cos65°=sin（65°-20°）=sin45°=22故选C．

3−sin70°2−cos210°=3−sin70°2−1+cos20°2=2(3−sin70°)3−cos 20°=2(3−cos20°)3−cos 20°=2故答案为：2

原式=3−sin(90°−20°)2−1+cos20°2=3−cos20°2−1+cos20°2=6−2cos20°4−1−cos20°=2(3−cos20°)3−cos20°=2．