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.
