Answer:
D. 5x^4 -37x^3 -6x^2 +41x -6
Explanation:
We really only need to look at the first and last terms to determine which answer choice to select.
The x^4 term in the sum will be ...
5x^4 -8x^4 -(-4x^3)(2x) = (5 -8 +8)x^4 = 5x^4
The constant term in the sum will be ...
(-1) +(2) -(-1)(-7) = -1 +2 -7 = -6
The only answer choice matching these first and last terms is Choice D.
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Additional comment
You can work out the other three terms as ...
-9x^3 -(-4x^3)(-7) = (-9 -28)x^3 = -37x^3
4x^2 -(5x)(2x) = (4 -10)x^2 = -6x^2
(7x) +(-3x) -(5x(-7) -1(2x)) = (7 -3 +35 +2)x = 41x
These all match choice D.