Verified answer

I think you have a typo. Should it be: 2xy^4 + 5xy^4 - 7xy^4?

If so, it might be easier to approach the problem if you say A = xy^4

Then, you have 2A + 5A - 7A

= A (2 + 5 - 7)

= A * 0 = 0

If you wrote it correctly: 2xy^4 + 5xy^4 - 7x^4y, then the answer is a bit different. Using the same A = xy^4, you have:

2A + 5A - 7x^4y

= 7A - 7x^4y

= 7 (A-x^4y)

Substitute xy^4 back into A

= 7 (xy^4 - x^4y)

Factor out an x and y

= 7xy (y^3 - x^3)

Hope that helps.

(2xy+9xy-7x)^4 +y

7x(y^4) - 7y(x^4)