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Question 980004: Hello, I'm currently studying for my accuplacer by using some study guides online that also provide a test at the end. I'm currently practicing factoring trinomials and on my test I got three answers wrong, which the answers seem to just be written in a different form than mine, but using foil on MY answers comes up with the original trinomial as well, so it would seem to be correct.
Long story short, I'm curious if I did something wrong, or simply came up with another viable solution and if my answer would be acceptable, say on a test. I'd like to provide all three questions just to clarify, but I understand the one problem rule, so please feel free to only address the first one, or give a simple yes or no if my answers would be acceptable.
First one: 21 + 4k^2 + -1k^4
What I came up with: -1(k^2 + 3)(k^2 + -7)
What they came up with: (3 + k^2)(7 + -1k^2)
Second one: 21 + 4k^2 + -1k^4
What I came up with: -1(k^2 + 3)(k^2 + -7)
What they came up with: (3 + k^2)(7 + -1k^2)
Third one: 3 + -10r^2 + 8r^4
What I came up with: (2r^2 + -1)(4r^2 + -3)
What they came up with: (1 + -2r^2)(3 + -4r^2)
Sorry if this is confusing, I just mainly want to know if my answer is ALSO acceptable, and if it's not, what method you used to come up with the "correct" answer they provided.
Answer by Alan3354(69443)   (Show Source):
You can put this solution on YOUR website! First one: 21 + 4k^2 + -1k^4
What I came up with: -1(k^2 + 3)(k^2 + -7)
What they came up with: (3 + k^2)(7 + -1k^2)
These are the same. -1*(k^2 - 7) = (7 - k^2)
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Second one: 21 + 4k^2 + -1k^4
What I came up with: -1(k^2 + 3)(k^2 + -7)
What they came up with: (3 + k^2)(7 + -1k^2)
Same again, same reason.
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Third one: 3 + -10r^2 + 8r^4
What I came up with: (2r^2 + -1)(4r^2 + -3)
What they came up with: (1 + -2r^2)(3 + -4r^2)
Same thing here, except both binomials are multiplied by -1.
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Your format is what's usually expected, in descending order of exponents.
Third one: 3 + -10r^2 + 8r^4 = 8r^4 - 10r^2 + 3
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What I came up with: (2r^2 + -1)(4r^2 + -3) --> (2r^2 - 1)*(4r^2 - 3)
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