Question 150601
{{{ graph( 700, 700, -8, 10, -10, 5, x^2 - 2x - 8) }}}
The crossings of the x-axis, {{{x = 4}}}, and {{{x = -2}}}
are the solutions, because those values both make
{{{x^2 - 2x - 8 = 0}}} true
Rewriting, {{{x - 4 = 0}}} and {{{x + 2 = 0}}} give me
the factors of the equation, since
{{{(x - 4)(x + 2) = x^2 - 2x - 8}}}
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The function has a minimum which is exactly midway between 
the roots. To find the x-coordinate of the midpoint, 
{{{(4 + (-2))/2 = 1}}}
Another way to find the x-coordinate of the vertex is  
to use the formula {{{(-b)/(2a)}}}, where 
{{{ax^2 + bx + c = 0}}} is the general formula
In this case, {{{a = 1}}}, {{{b = -2}}}
{{{(-b)/(2a) = -(-2)/(2*1) = 1}}}