Question

Bài Tìm x,biết

a) (x-1)^3+(2-x)(4+2x+x^2)+3x(x+2)=16

b) (x+2)(x²-2x+4)-x(x²-2)=16

c) x(x-5)(x+5)-(x+2)(x²-2x+4)=17

d)(x-3)³-(x-3)(x²+3x+9)+9(x+1)²=15

Answer 1

a) (x - 1)³ + (2 - x)(4 + 2x + x²) + 3x(x + 2) = 16

x³ - 3x² + 3x - 1 + 8 - x³ + 3x² + 6x - 16 = 0

9x - 9 = 0

9x = 9

x = 1

Vậy x ∈ {1}

b) ( x + 2)(x² - 2x + 4) - x(x² - 2) = 16

x³ + 8 - x³ + 2x - 16 = 0

2x - 8 = 0

2x = 8

x = 4

Vậy x ∈ {4}

c) x(x - 5)(x + 5) - (x + 2)(x² - 2x + 4) = 17

x³ - 25x - x³ - 8 - 17 = 0

-25x - 25 = 0

-25x = 25

x = -1

Vậy x ∈ {1}

d) (x - 3)³ - (x - 3)(x² + 3x + 9) + 9(x + 1)² = 15

x³ - 9x² + 27x - 27 - x³ + 27 + 9x² + 18x + 9 - 15 = 0

45x - 6 = 0

45x = 6

x = \(\frac{2}{15}\)

Vậy x ∈ {\(\frac{2}{15}\)}