n=1,Q=0.04
n=2,Q=0.08
n=3,Q=0.12
n=4,Q=0.16
所以Q/n=0.04
Q=0.04n
n=150,Q=0.04*150=6
Q=0.04,A=20-0.04
Q=0.08,A=20-0.08,
……
所以A=20-Q
所以Q=6,A=20-Q=20-6=14升
x=-3,y=1/2
(x+y)^2=(-3+1/2)^2=(-5/2)^2=25/4
x^2+2xy+y^2=(-3)^2+2*(-3)*(1/2)+(1/2)^2=9-3+1/4=25/4
x=1/3,y=-1/5
(x+y)^2=[1/3+(-1/5)]=(1/3-1/5)^2=(2/15)^2^2=4/225
x^2+2xy+y^2=(1/3)^2+2*(1/3)*(-1/5)+(-1/5)^2=1/9-2/15+1/25=4/225