由a2+b2+c2+338=10a+24b+26c,得:(a2-10a+25)+(b2-24b+144)+(c2-26c+169)=0,即:(a-5)2+(b-12)2+(c-13)2=0,由非负数的性质可得: a?5=0 b?12=0 c?13=0 ,解得: a=5 b=12 c=13 ,∵52+122=169=132,即a2+b2=c2,∴∠C=90°,则三角形ABC为直角三角形.