n10*sin30*sin50*sin70=?2.求y=3sinx+1/sinx+2的最大值和最小值3.已知sin(pi/4-x)=5/13,0<x 1:sin10sin30sin50sin70=sin20sin30sin50sin70/2cos10=sin20cos20sin50sin70/2cos10=sin40sin50/4cos10=sin40cos40/4cos10=sin80/8cos10=cos10/8cos10=1/82:ysinx+2y=3sinx+1,所以sinx=(1-2y)/(y-3),因為-1≤sinx≤1,所以-1≤(1-2y)/(y-3)≤1,所以解得:-2≤y≤4/33:cos2x/cos(x+45)=[cosx^2-sinx^2]/[√2/2(cosx-sinx)]=(cosx+sinx)(cosx-sinx)/[√2/2(cosx-sinx)]=√2(cosx+sinx)=2sin(x+45)因為0熱心網友
