Question 290002
{{{ graph( 300, 300, -10, 10,-90, 10, -(1/2)*x^2-1) }}}
The parabola is in vertex form already (because it has no x term). 
{{{y=-(1/2)*(x-0)^2-1}}}
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Here's the graph with {{{y=-x^2}}} added. 
{{{ graph( 300, 300, -10, 10, -90, 10, -(1/2)*x^2-1, -x^2) }}}
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{{{ graph( 300, 300, -10, 10, -10, 90,4x^2, x^2/4,2x^2) }}}
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{{{y=4x^2}}} is in green.
{{{y=(1/4)x^2}}} is in red.
{{{y=2x^2}}} is in blue.