a^2+b^2=_(a+b)^2-2ab=9-4=5____,(a-b)^2=a^2+b^2-2ab=5-4=1_____祝学习进步
a+b=-3，（a+b）^2=9，a^2+b^2=（a+b）^2-2ab=9-4=5(a-b)^2=（a+b）^2-4ab=9-8=1
