Question

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Answer 1

First, you cannot factor this since the notation is not correct. If you want to show an exponent, you should use something like this:

400x^8 - 36

That being said, this is the difference of two squares 20x^4 and 6. So the answer is

(20x^4 +6) (20x^4 -6).

But you are not quite complete. Notice that a factor of 2 can be taken for each leaving:

(4)(10x^4+3)(10x^4 -3)

Hope that helps.

(Also you could take the 4 factor out first leaving:
(4)(100x^8 - 9)
And then factor the second factor as a difference of two squares, leaving you with the same answer.

Answer 2

You are welcome!