Answer :

konrad509
[tex]81x^4-1=\\ (9x^2)^2-1^2=\\ (9x^2+1)(9x^2-1)=\\ (9x^2+1)((3x)^2-1^2)=\\ (9x^2+1)(3x+1)(3x-1)[/tex]
eu99li


Using this: a²-b²=(a+b)(a-b)

81x^4-1=

(9x²)²-1=

(9x²-1)(9x²+1)=      (in the bold half we use the formula again)

(3x+1)(3x-1)(9x²+1)

So the answer is D


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