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Toán Lớp 8: Tìm x, biết : a, x ³ + 15x ² + 75x + 125 = 0 b, x ³ + 48x = 12x ² + 64 c, ( 5x – 1 ) – 196 = 0 d, 1/27x ³ – 1/3x ² + x = 1

Home/ Toán Lớp 8: Tìm x, biết : a, x ³ + 15x ² + 75x + 125 = 0 b, x ³ + 48x = 12x ² + 64 c, ( 5x – 1 ) – 196 = 0 d, 1/27x ³ – 1/3x ² + x = 1

Toán Lớp 8: Tìm x, biết : a, x ³ + 15x ² + 75x + 125 = 0 b, x ³ + 48x = 12x ² + 64 c, ( 5x – 1 ) – 196 = 0 d, 1/27x ³ – 1/3x ² + x = 1

Hoa Tháng Bảy 5, 2022 Toán học 1 Comment 0 views

Toán Lớp 8: Tìm x, biết :
a, x ³ + 15x ² + 75x + 125 = 0
b, x ³ + 48x = 12x ² + 64
c, ( 5x – 1 ) – 196 = 0
d, 1/27x ³ – 1/3x ² + x = 1

Comments ( 1 )

minhtamnguyet88
5 Tháng Bảy, 2022 at 3:44 sáng

Reply

a, x^3 + 15x^2 + 75x + 125 = 0

x^3 + 3 . x^2 . 5 + 3 . x . 5^2 + 5^3 = 0

(x + 5)^3 = 0

x + 5 = 0

x = -5

b, x^3 + 48x = 12x^2 + 64

x^3 – 12x^2 + 48x – 64 = 0

x^3 – 3 . x^2 . 4 + 3 . x . 4^2 – 4^3 = 0

(x – 4)^3 = 0

x – 4 = 0

x = 4

c, (5x – 1) – 196 = 0

5x – 1 = 196

5x = 197

x = 197/5

d, 1/(27x^3) – 1/(3x^2) + x = 1

1/(27x^3) – 1/(3x^2) + x – 1 = 0

[1/(3x)^3] – 3 . 1/(9x^2) . 1 + 3 . 1/(3x) . 1^2 – 1^3 = 0

[1/(3x) – 1]^3 = 0

1/(3x) – 1 = 0

1/(3x) = 1

3x = 1

x = 1/3

Gửi bạn

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