Question 7475
Look at them together:

{{{system( 4x^2-2x+7, 2x-4x^2-7) }}}

rewrite the second to have terms in the same order

{{{system( 4x^2-2x+7, -4x^2+2x-7) }}}

you can see that the second expression is the opposite of the first. 

So, 

{{{-4x^2+2x-7 = -f(x)}}}