a=(m,n),b=(cosx,sinx)因为|a|=4|b|所以(|a|)^2=16(|b|)^2m^2+n^2=16[(cosx)^2+(sinx)^2]所以m^2+n^2=16所以可设m=4cosy,n=4siny(y属于[0,pai/2])a*b=mcosx+nsinx=4(cosycosx+sinysinx)=4cos(x-y)所以a*b的取值范围...