(x-2)(x+2)-(x-2)^2=x^2-4-(x^2-4x+4)=x^2-4-x^2+4x-4=4x-8把x=-1/4代入得：4x-8=4*(-1/4)-8=-9
[x-2][x+2]-[x-2]²=x²-4-(x²-4x+4)=4x-8当x=-¼时原式=-1-8=-9
