(x+y)^2=x^2+y^2=2xy所以碧亏:x^2+y^2=(x+y)^2-2xy=12.5(x^2+y^2)/(2)-xy=(x^2+y^2-2xy)脊纳/樱慧没2=(x-y)^2/2=4.5
25/2,9/2
12.5,4.5
x^2+y^2=(x+y)^2-2xy=16-7/2=25/羡手隐兄厅2(x^2+y^2)/(2)-xy=1/2[(x-y)^2]=9/薯祥2