[tex](x+3)^2=x^2+7x\\\\x^2+2\cdot x\cdot3+3^2=x^2+7x\\\\x^2+6x+9=x^2+7x\\\\x^2+6x-x^2-7x=-9\\\\-x=-9 \ \ |:(-1)\\\\\huge\boxed{x=9}[/tex]
[tex](x+3)^{2} = x^{2}+7x\\\\x^{2}+6x+9 = x^{2}+7x\\\\x^{2}-x^{2} + 6x - 7x= -9\\\\-x = - 9 /:(-1)\\\\x = 9[/tex]
