4/3 + -11/31 + 3/10 - 20/31 - 2/5

= (4/3 + 3/10 - 2/5) - (11/31 + 20/31)

= (40/30 + 9/30 - 12/30) - 1

= (49/30 - 12/30) - 1

= 37/30 - 30/30

= 7/30

d) ( 2x - 15)^5 = (2x -15)^3

(2x - 15)^5 - (2x - 15)^3 = 0

(2x - 15)^3.[(2x - 15)^2 - 1] = 0

2x - 15 = 0, 2x = 15, x = 15/2

(2x - 15)^2 - 1 = 0

(2x - 15)^2 = 1

2x - 15 = -1 hoặc 2x - 15 = 1

2x - 15 = -1

2x = -1 + 15

2x = 14

x = 14/2

x = 7

2x - 15 = 1

2x = 1 + 15

2x = 16

x = 16/2

x = 8

Vậy x ∈ 7; 15/2; 8}

c) x^10 = x

x^10 - x = 0

x(x^9 - 1) = 0

x = 0 hoặc x^9 - 1 = 0

x^9 = 1

x = 1

Vậy x ∈ {0; 1}

2. Tìm x:

a) 4x = 2x+1

4x - 2x = 1

2x = 1

x = 1/2

Vậy x = 1/2

b) 16 = (x-1)^4

2^4 = (x - 1)^4

x - 1 = - 2 hoặc x - 1 = 2

x - 1 = -2, x = -2 + 1, x = -1

x - 1 = 2, x = 2 + 1, x = 3

Vậy x ∈ {-1; 3}

1. Tính:

B= 12 . 108+ 17 . 107

B = 1296 + 1819

B = 3115

(3n + 1) ⋮ 2n

(6n + 2) ⋮ 2n

2 ⋮ 2n

1 ⋮ n

n ∈ Ư(1) = {-1; 1}

Vậy n ∈ {-1; 1}

(3n + 1) ⋮ 2n

(6n + 2) ⋮ 2n

2 ⋮ 2n

1 ⋮ n

n ∈ Ư(1) = {-1; 1}

Vậy n ∈ {-1; 1}