[tex](5x+1)^2-25x=31\\\\25x^2+10x+1-25x-31=0\\\\25x^2-15x-30=0|:5\\\\5x^2-3x-6=0\\\\a=5\\b=-3\\c=-6\\\\\Delta=b^2-4ac\\\\\Delta=(-3)^2-4\cdot5\cdot(-6)=9+120=129\\\\x_1=\frac{-(-3)-\sqrt{129} }{2\cdot5} =\frac{3-\sqrt{129} }{10}\\ \\x_2=\frac{-(-3)+\sqrt{129} }{10}=\frac{3+\sqrt{129} }{10}[/tex]
