f（x）=2sin（π/4x+π/4）

　　y=f(x)+f(x+2)

　　=2sin（π/4x+π/4）+2sin[π/4(x+2)+π/4]

　　=2sin（π/4x+π/4）+2sin[π/4x+π/2+π/4]

　　=2sin（π/4x+π/4）+2cos（π/4x+π/4)

　　=2√2[√√2/2*sin（π/4x+π/4）+√2/2*cos（π/4x+π/4)]

　　=2√2sin[(π/4*x+π/4)+π/4]

　　=2√2sin(π/4*x+π/2)

　　=2√2cos(π/4*x)

　　∵x∈[-6,-2/3]

　　∴-3π/2≤π/4x≤-π/6

　　∴当-3π/2≤π/4x≤-π,即x∈[-6,-4]时,函数递减,

　　当-π≤π/4x≤-π/6,即x∈[-4,-2/3]时,函数递增