Question 498286
{{{ 2x^4 - 18x^2 = 0 }}}
{{{ 2x^2*( x^2 - 9 ) = 0 }}}
This is true if either:
{{{ x = 0 }}} or
{{{ x^2 - 9 = 0 }}}
{{{ x^2 = 9 }}}
{{{ x = 3 }}} 
{{{ x = -3 }}}
This is a 4th degree equation, so there should be 4 roots
The {{{ x = 0 }}} is called a "double root", so the 4 roots are
{{{ x = 0 }}}
{{{ x = 0 }}}
{{{ x = 3 }}}
{{{ x= -3 }}}