Question 27341
Looks fine to me.  You're just distributing the {{{-2x^2}}} to the other 3 terms in the trinomial {{{3x^2-4x+5}}}.

So you multiply each term (not forgetting your signs) and think at each step...
{{{-2x^2*3x^2=-6x^4}}}
{{{-2x^2*-4x=8x^3}}}
{{{-2x^2*5=-10x^2}}}
So adding all three terms together you have:
{{{-6x^4+8x^3-10x^2}}}