Toán Lớp 8: bài 1
(3x^n+1-2x^n).4x^2
bài 2 rút gọn biểu thức
a)-2x(x+1)+(2x-3).(x-2)
b)(2x-3).(2x-+3)-4x(x-1)+9
c)9x(3x^2-5x)-(3x+1).(9x^2-18x-1)
d)3x^n(6x^n-3+1)-2x^n(9x^n-1)
e)5(3x-4y^3)+(9(2x^2-y^3)-2(x^2-y^3)
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Toán Lớp 8: bài 1
(3x^n+1-2x^n).4x^2
bài 2 rút gọn biểu thức
a)-2x(x+1)+(2x-3).(x-2)
b)(2x-3).(2x-+3)-4x(x-1)+9
c)9x(3x^2-5x)-(3x+1).(9x^2-18x-1)
d)3x^n(6x^n-3+1)-2x^n(9x^n-1)
e)5(3x-4y^3)+(9(2x^2-y^3)-2(x^2-y^3)
Comments ( 2 )
Bài 1:
$ (3x ^ n + 1 – 2x ^ n) \times 4x ^ 2 \\= (x ^ n (3 – 2) + 1) \times 4x ^ 2 \\= (x ^ n + 1) ^
\times 4x ^ 2 \\= 4x ^{n + 2} + 4x ^ 2 $
Bài 2:
a) $ – 2x (x + 1) + (x – 2) (2x – 3) \\= ( – 2x ^ 2 – 2x) + ( 2x ^ 2 – 7x + 6) \\= – 9x + 6$
b) $ (2x – 3) (2x + 3) – 4x (x – 1) + 9 \\= 4x ^ 2 + 9 + ( – 4x ^ 2 + 4x) + 9 \\= – 4x + 18$
c) $ 9x (3x ^ 2 – 5x) – (3x + 1) (9x ^ 2 – 18x – 1) \\= (27x ^ 3 – 45x ^ 2) – (27 x ^ 3 – 45 x ^ 2 + 6x – 1) \\= – 6x + 1$
d) $ 3x ^ n (6x ^ n – 2) – 2x ^ n (9x ^ n – 1) \\= 18x ^{2n} – 6x ^ n – 18x ^{2n} + 2x ^ n \\= – 4x ^ n $
e) $ 5 (3x – 4y ^3) + (9 (2x ^ 2 – y ^ 3) – 2 (x ^ 2 – y ^ 3) ) \\= (15x – 20y ^ 3) + ( (18x ^ 2 – 9y ^ 3) + ( – x ^ 2 +2 y ^ 3) ) \\= 17 x ^ 2 – 27 y ^ 3 + 15x$