x^2-10x+y^2+4y+29=0
x^2-10x+25+y^2+4y+4=0
(x-5)^2+(y+2)^2=0
故 x-5=0 y+2=0
所以 x=5 y=-2
那么x^2+y^2=5^2+(-2)^2=25+2=29