a^2+ab=3,ab+b^2=7
a^2+ab+ab+b^2=7+3=10=a^2+2ab+b^2=(a+b)^2
（a+b）^2=10,则,a+b=√10
a^2=2ab+b^2,a^2=√10+b^2+ab=√10 +7