Вправа 881 алгебра Бевз гдз 7 клас
№ 881
a) (x2 – 4)2 – х4 = 8(х2 – 4 – х2)(х2 – 4 + х2) = 8
–4 • (2х2 – 4) = 8;
b) (x + 3)2 – (x – 3)2 = 12
(х + 3 – х + 3)(х + 3 + х – 3) = 12
6х2 = 12;
c) (2х – 1)(4x2 + 2x + 1) = х(3х – 2)(3х + 2) – x3
8х3 – 1 = 9х3 – 4х – х3
–4х = 1
х = 0,25
d) (2х – 3) (4x2 + 6x + 9) = 7(х3 – 4)
8х3 – 27 = 7х3 – 28
х3 = –1;
е) (3,7х – 2)(3,7x + 2) – (1,3х – 1)(1,3x + 1) = 6х(2х – 1)
13,69х2 – 4 – (1,69х2 – 1) = 12х2 – 6х
12х2 – 3 = 12х2 – 6х
–6х = –3
х = –3 : (–6)
х = 0,5.
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