a-b=3,ab=2a^2-2ab+b^2=9a^2+b^2=9+2aba^2+b^2=9+2*2a^2+b^2=13
a^2+b^2=(a-b)^2+2ab=3^2+4=13
a=b+3代入ab=2可求啊、b的值
a^2+b^2=(a-b)^2+2ab=9+4=11
a^2+b^2=(a-b)^2+2ab=3^2+2*2=9+4=13