`5x(x-2015)-x+2015=0`
`⇔5x(x-2015)-(x-2015)=0`
`⇔(x-2015)(5x-1)=0`
\(⇔\left[ \begin{array}{l}x-2015=0\\5x-1=0\end{array} \right.\)
\(⇔\left[ \begin{array}{l}x=2015\\x=\dfrac{1}{5} \end{array} \right.\)
`2,`
`86^2+172.14^2`
`=86^2+2.86.14+14^2`
`=(86+14)^2`
`=100^2`
`=10000`