Question 598931
{{{ (5x)^2=(5x-3)^2+(x+6)^2 }}}
{{{ 25x^2 = 25x^2 - 30x + 9 + x^2 + 12x + 36 }}}
Subtract {{{ 25x^2 }}} from both sides
{{{ 0 = x^2 - 18x + 45 }}}
{{{ ( x - 3 )*( x - 15 ) = 0 }}}
{{{ x = 3 }}} or {{{ x = 15 }}} should work