1.f(x)=cosx-1/2cos2x f(x)=cosx-1/2(2os^2 x-1) f(x)=cosx-cos^2 x+1/2 f(x)=-(cosx-1/2)^2+3/4 当cosx=1/2时,f(x)最大,最大值为3/42.sin10·sin30·sin50·sin70=cos80*cos40*cos20*sin30=2sin20*(cos20*2*cos40*2...