Final answer:
The expression to be completely simplified is x^4 - 4x^2 - 6x^3 + 24x - 7x^2 + 28. The simplified expression is x^4 - 6x^3 - 11x^2 + 24x + 28.
Step-by-step explanation:
The expression to be completely simplified is: x^4 - 4x^2 - 6x^3 + 24x - 7x^2 + 28.
First, we can combine like terms: -6x^3 + x^4 - 7x^2 - 4x^2 + 24x + 28.
Next, we can rearrange the terms in descending order of degree: x^4 - 6x^3 - 11x^2 + 24x + 28.
Therefore, the simplified expression is: x^4 - 6x^3 - 11x^2 + 24x + 28.