a^2+b^2-10a+6b+34=0
a²-10a+25+b²+6b+9=0
(a-5)²+(b+3)²=0
∴(a-5)²=0,(b+3)²=0
a-5=0,b+3=0
a=5,b=-3.
5a-3b
=5×5-3×(-3)
=25+9
=34