Question

Calculati:
81a la a patra - 1=?
(doar ''a'' e la a patra)

Answer 1

$81a^4 -1 = 9^2\cdot a^4 - 1 = 9^2\cdot {(a^2)}^2 -1 = \\ \\ = \Big (9\cdot a^2\Big)^2 -1 = (9a^2-1)(9a^2+1)= \\ \\ = \Big((3a)^2 - 1\Big)\Big(9a^2+1\Big) =\\ \\ = (3a-1)(3a+1)(9a^2+1)$

Answer 2

foto
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