a^2+b^2+c^2+50=6a+8b+10c,
a^2+b^2+c^2-6a-8b-10c+50=0,
a^2-6a+9+b^2-8b+16+c^2-10c+25=0,
(a-3)^2+(b-4)^2+(c-5)^2=0,
a=3,b=4,c=5
勾股定理逆定理,判断是直角三角形