Question 1198618
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I assume you want to expand that out. In the future, please post the verbal instructions.


{{{y = (x+5)(x^2+3x+4)}}}


{{{y = w(x^2+3x+4)}}} Let w = x+5


{{{y = wx^2+3wx+4w}}} Distribute


{{{y = x^2(w)+3x(w)+4(w)}}} 


{{{y = x^2(x+5)+3x(x+5)+4(x+5)}}} Plug in w = x+5  


{{{y = (x^3+5x^2)+(3x^2+15x)+(4x+20)}}}  Distribute three times more


{{{y = x^3+8x^2+19x+20}}}  Combine like terms


Therefore,
{{{(x+5)(x^2+3x+4) = x^3+8x^2+19x+20}}}
is an identity, i.e. it is a true equation for all real numbers x.
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