(1）（x+q）*（x+1/5）=x^2+(q+1/5)x+q/5
q+1/5=0
q=-1/5
(2)(3m+2n)*(3m+2n+m-n)=(3m+2n)*(2m+n)=6m^2+7mn+2n^2
(3)(x+y-z）*（x+y+z）=(x+y)^2-z^2=x^2+y^2-z^2+2xy
(4)（1+1/2）*（1+1/2^2）*（1+1/2^4）*（1+1/2^8）
=(1+1/2+1/4+1/8)*(1+1/2^4+1/2^8+1/2^12)
=1*(1-1/2^4)/(1-1/2)*1*(1-1/2^16)/(1-1/2^4)
=(15/8)*