(1-√x)^6 (1+√x)^2=(1-x)^2(1-√x)^4=(1-2x+x^2)(1-2√x+x)^2=(1-2x+x^2)(1-2√x+x-2√x+4x-2x√x+x-2x√x+x^2)=(1-2x+x^2)(1-4√x+6x-4x√x+x^2)=(1-4√x+6x-4x√x+x^2)-2x(1-4√x+6x-4x√x+x^2)+x^2(1-4√x+6x-4x√x+x^2)=……
x的系数:(1-4√x+【6x】-4x√x+x^2)-【2x】(【1】-4√x+6x-4x√x+x^2)+x^2(1-4√x+6x-4x√x+x^2)
即6-2=4.