[tex]\text{use}\ (a+b)^2\equiv a^2+2ab+b^2\\\\(x+a)^2-7\equiv x^2+10x+b\\\\x^2+2xa+a^2-7\equiv x^2+10x+b\\\Downarrow\\2a=10\ and\ b=-7\\\\\boxed{a=5\ and\ b=-7}[/tex]
