计算:(3x+1)^2 (3x-1)^2-(2x+1)(-2x+1)

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计算:(3x+1)^2 (3x-1)^2-(2x+1)(-2x+1)
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计算:(3x+1)^2 (3x-1)^2-(2x+1)(-2x+1)
计算:(3x+1)^2 (3x-1)^2-(2x+1)(-2x+1)

计算:(3x+1)^2 (3x-1)^2-(2x+1)(-2x+1)
原式=(3x+1)^2 (3x-1)^2+(2x+1)(2x-1)
=(3x+1)^2 (3x-1)^2+4x^2-1
=(9x^2+1+6x)(9x^2+1-6x)+4x^2-1
=81x^4-54x^3+9x^2+9x^2-6x+1+54x^3-36x^2+6x+4x^2-1
=81x^4-14x^2

(3x+1)^2 (3x-1)^2-(2x+1)(-2x+1)
=(9x^2-1)^2-(1-4x^2)
=81x^4-18x^2+1-1+4x^2
=81x^4-14x^2
=x^2(81x^2-14)

注意符号
={(3x)^2 - 1} + {(2x)^2 - 1}
=9x^2 -1 + 4x^2 -1
=13x^2 -2

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