Question 32089
{{{ c^2 - 4 = 0 }}}
This is the difference of two squares.  Get used to seeing this ... A LOT!!
Memorize this form:
{{{ (x+y)(x-y)=x^2 - y^2 }}}
In this case ... the c is the x value and the 4 is the y value.
{{{ (c-2)(c+2)=0 }}} 
set each piece equal to 0
{{{ c-2 = 0 }}} and {{{ c+2=0 }}}
{{{ c=2 }}} and {{{ c = -2 }}}