若(x+1)2+(y-2)2=0,则x2+y2=_;若a2+b2-4a+2b+5=0,则ab=_.
问题描述:
若(x+1)2+(y-2)2=0,则x2+y2=______;若a2+b2-4a+2b+5=0,则ab=______.
答
(1)因为(x+1)2+(y-2)2=0,所以x=-1,y=2,则x2+y2=1+4=5;
(2)因为a2+b2-4a+2b+5=0,所以a2-4a+4+b2+2b+1=0,即(a-2)2+(b+1)2=0,则a=2,b=-1.因此ab=2×(-1)=-2.