设向量a=(1,2),b=(2,3),若向量xa+b与向量c=(-4,-7)共线,则x=

(1)设xa+b=Ac
则x+2=-4A
2x+3=-7A
解得x=2,A=-1
(2)f(x)=√3sinx+sin(π/2+x)=√3sinx+cosx=2(√3/2sinx+1/2cosx)
=2sin(x+π/6)
当x+π/6=π/2+2kπ时,即x=π/3+2kπ时
f(x)max=2