解三角方程:sin40sin(50-x)=sin70sinx(角的单位:度),求其通解。 →sin40°sin(50°-x)=sinxcos20° →2sin20°sin(50°-x)=sinx →cos(x-30°)=sinx+sin(x+20°) →sin(x+60°)-sinx=sin(x+20°) →2cos(x+30°)sin30°=sin(x+20°) →cos(x+30°)-cos(70°-x)=0 →-2sin50°sin(x-20°)=0 →sin(x-20°)=0 →x-20°=k*180°, 即x=20°+k*180°(k∈Z) 第二个方程: sin80°sin(x-10°)=sinxsin50° 解答—— 2sin40sin(x-10)=sinx cos(x-50)-cos(x+30)=sinx 方法一: cos(x-50)-sinx=cos(x+30) sin(40+x)-sinx=cos(x+30) 2cos(20+x)sin20=cos(x+30) (行不通) 方法二: cos(x-50)=cos(x+30)+sinx cos(x-50)=sin(60-x)+sinx cos(x-50)=2sin30cos(30-x) cos(x-50)-cos(x-30)=0 -2sin(x-40)sin(-10)=0 sin(x-40)=0 x-40=k*180 x=40+k*180 |
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