sin20sin40sin80求值...

sin20sin40sin80*(sin60)=-1/2(cos60-cos20)sin80*(根号3/2)=-1/4*sin80+1/2*[1/2*(sin60+sin100)]*根号3/2 =(-1/4*sin80+1/4*sin60+1/4*sin100)*根号3/2 =1/4*根号3/2*根号3/2 =3/16

= (4sin20cos20 + sin20) /cos20 = (2sin40 + sin20)/cos20 = (sin40 + sin40 + sin20)/cos20 = (sin40 + 2sin(40+20)/2 * cos(40-20)/2 ) /cos20 = (sin40 + 2sin30*cos10 ) /cos20 = (sin40 + cos10)/cos20 = (sin40 + sin80)/cos20 = 2sin(40+80)...

主要考查了倍角公式sin2a=2sinacosa cos20°cos40°cos80° =(2sin20°cos20°)cos40°cos80°/2sin20° =sin40°cos40°cos80°/2sin20° = (2sin40°cos40°)cos80°/4sin20° =sin80°cos80°/4sin20° =2 sin80°cos80°/8sin20° =sin 160°/8sin20° =sin20°/8sin20...

=（cos20cos40cos80）/1; 分子分母同时乘以2sin20 =(2sin20*cos20*cos40*cos80)/2sin20;运用2倍角公式：2sin20cos20=sin40；=（sin40*cos40*cos80）/2sin20;分子分母同时乘以2，=（2sin40*cos40*cos80）/4sin20；再用2倍角公式 =sin80*cos80/4sin20;分子分母同时乘以2，=2sin...

sin31=0.5150380749100542 sin32=0.5299192642332049 sin33=0.544639035015027 sin34=0.5591929034707468 sin35=0.573576436351046 sin36=0.5877852522924731 sin37=0.6018150231520483 sin38=0.6156614753256583 sin39=0.6293203910498375 sin40=0.6427876096865392 sin41=0.656059028990507...

-sin1º=0.0175 sin2º=0.0349 sin3º=0.0523 sin4º=0.0698 sin5º=0.0872sin6º=0.1045 sin7º=0.1219 sin8º=0.1392 sin9º=0.1564 sin10º=0.1736sin20º=0.3420 sin30º=0.5000 sin40º=0.6428 sin50º=0.7660 sin60º=0.8660sin70º=0.9397 sin80º=0.9848例:求sin33...

Cos20cos40cos80sin20 =sin40cos40cos80/2sin20 = sin80cos80 /4sin20 =sin160 /8sin 20 =sin(180-20)/8sin20 =sin20/8sin20 =1/8 分子分母同乘同除sin20 就好算了 上面是详细的过程 根据：sin2A=2sinAcosB

解：原式=(sin20°cos20°cos40°cos80°)/sin20° =(sin40°cos40°cos80°)/(2sin20°)=(sin80°cos80°)/(4sin20°)=sin160°/(8sin20°)=1/8

tan20+4sin20 =sin20/cos20+4sin20 =(sin20+4sin20cos20)/cos20 =(sin20+2sin40)/cos20 =(sin20+sin40+sin40)/cos20 =(2sin30cos10+sin40)/cos20 =(cos10+sin40)/cos20 =(sin80+sin40)/cos20 =2sin60cos20/cos20 =2sin60 =根号3 ...

有一个公式 sinθsin(60-θ)sin(60+θ)=1/4sin3θ 所以=sin60(sin20sin(60-20)sin(60+20))=sin60^2/4 =3/16 不然就要先积化合差，再和差化积 sin20sin40sin60sin80 =sin60[0.5sin20(cos40-cos120)]=sin60(0.5sin20cos40+0.25sin20)=sin60(0.25sin60-0.25sin20+0....