If you would like to write -2x^2 (-5x^2 + 4x^3) in standard form, you can do this like this:
Writing the polynomial in standard form means that you have to write the terms by descending degree:
-2x^2 (-5x^2 + 4x^3) = 2 5 x^2 x^2 - 2 4 x^2 x^3 = 10 x^4 - 8 x^5 = - 8x^5 + 10x^4
The correct result would be - 8x^5 + 10x^4.
