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anonymous

  • one year ago

Factor completely: 81x4 – 81 A. (9x2 + 9)(3x + 3)(3x – 3) B. (3x + 3)2(3x – 3)2 C. (3x + 3)(3x – 3) D. (9x2 + 9)(9x2 – 9)

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  1. anonymous
    • one year ago
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    \[81x^4-81?\]

  2. SolomonZelman
    • one year ago
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    \(81x^4 – 81\) \(81(x^4 –1 )\) \(81(~(x^2)^2 –1^2 )\) \(81(x^2 –1 )(x^2+1)\) and then the last step...

  3. SolomonZelman
    • one year ago
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    this is how I would go about this problem, with no need to remember any identities with the 4th power.

  4. anonymous
    • one year ago
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    thanks @SolomonZelman

  5. SolomonZelman
    • one year ago
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    not done yet, you need one more step to complete this problem

  6. SolomonZelman
    • one year ago
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    oh, they did it differently, they didn't take 81 out....

  7. SolomonZelman
    • one year ago
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    oh, typo in the rule ok, so 81•x\(^4\)=3\(^4\)•x\(^4\)=(3x)\(^4\) this is what you get from your initial expression: (3x)\(^4\)-3\(^4\) then you can factor it, using a rule a\(^4\)-b\(^4\)=(a-b)(a+b)(a²+b²)

  8. SolomonZelman
    • one year ago
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    your a is 3x your b is 3

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