sin220等于多少
谁知道sin220是多少 -
sin220=-sin40
所以，Sin220=Sin(180+40)
sin220=-sin40
所以，Sin220=Sin(180+40)
=sin(220°)。
即sin220�0�2+cos250�0�2+sin20�0�2cos50�0�2=3/4
sin220(tan10-3)怎么做? -
sin220(tan10-根号3)=-sin40°（sin10°-根号3cos10°）cos10° =-sin40°×2sin(10°-60°)/cos10° =-sin40°×(-2sin50°)/cos10° =-sin40°×(-2cos40°)/cos10° =sin80°/cos10° =cos10°/cos10° =1
=sin²20°+[cos(20°+30°)]²+sin20°[cos(20°+30°)]=sin²20°+(√3/2cos20°-1/2sin20°)²+sin20(√3/2cos20°-1/2sin20°)=sin²20°+3/4cos²20-√3/2sin20°cos20°+1/4sin²20°+√3/2sin20°cos20°-1/2sin²希望你能满意。
求sin220°+cos250°+sin20°cos50°的值. -
解： 原式＝1/2(1－cos40°)＋1/2(1＋cos100°）＋sin20°cos50° ＝1＋1/2(cos100°－cos40°)＋1/2(sin70°－sin30°)＝3/4－sin70°sin30°＋1/2sin70° ＝3/4
sin²10°+sin²20°+√3sin10°sin20° =(1-cos20°)/2+(1-cos40°)/2+(√3/2)(cos10°-cos30°)=(4-√3)/4-cos30°cos10°+(√3/2)cos10° =(4-√3)/4-(√3/2)cos10°+(√3/2)cos10° =(4-√3)/4。
cos140°cos20°-sin220°sin20° -
cos140°cos20°-sin220°sin20°=cos140°cos20°-sin(360°-140°)sin20° =cos140°cos20°+sin140°sin20° =cos120°=-1/2
原式=(-cos40)cos20-(-sin40)sin20 =-(cos40cos20-sin40sin20)=-cos(40+20)=-1/2