Question

M =(lx+2l -lxl +2)(lx+2l -lxl -2)的取值范围

Answer 1

t=lx+2l -lxl

t^2=(x+2)^2+x^2-2lx^2+2xl =2x^2+4x-2lx^2+2xl+4

n=x^2+2x

m=(t+2)(t-2)=t^2-4=2n-2lnl

n≥-1

n≥0时

m=2n-2n=0

当n＜0时

m=4n

-4≤m≤0