Question

[tran tung]

Bài 1: Làm tính nhân

a) -3x^2 . ( 2x^3 - 2x + 1/3 )

b) ( x^4 + 2x^3 - 2/3 ) . ( -3x^4 )

c) ( x + 3 ) . ( x - 4 )

d) ( x - 4 ) . ( x^2 + 4x + 16 )

e) 4. ( x - 1/2 ) . ( x + 1/2 ) . ( 4x^2 + 1 )

Bài 2: Tìm x, biết

a) ( 2 - x ) . (x^2 + 2x + 4 ) + x . ( x - 3 ) . ( x + 4 ) - x^2 + 24 = 0

b) (x/2 + 3 ) . ( 5 - 6x ) + ( 12x - 2 ) . ( x/4 + 3 ) = 0

Answer 1

[Edogawa Conan]

1a) -3x²(2x³ - 2x + 1/3) = -6x⁵ + 6x³ - x²

b) (x⁴ + 2x³ - 2/3).(-3x⁴) = -3x⁸ - 6x⁷ + 2x⁴

c) (x + 3)(x - 4) = x² - 4x + 3x - 12 = x² - x - 12

d)(x - 4)(x² + 4x + 16) = (x - 4)(x² + 4x + 4²) = x³ - 64

e) 4(x - 1/2)(x + 1/2)(4x² + 1) =4(x² - 1/4)(4x²  + 1) = 4(4x⁴ + x² - x² - 1/4) = 4(4x⁴ - 1/4) = 16x⁴ - 1

B2. a) (2 - x)(x² + 2x + 4) + x(x - 3)(x + 4) - x² + 24 = 0

=> 8 - x³ + x(x² + 4x - 3x - 12) - x² + 24 = 0

=> 8 - x³ + x³ + x² - 12x - x² + 24 = 0

=> -12x + 32 = 0

=> -12x = -32

=> x = -32 : (-12) = 8/3

b) (x/2 + 3)(5 - 6x) + (12x - 2)(x/4 + 3) = 0

=> 5x/2 - 3x² + 15 - 18x + 3x² + 36x - x/2 - 6 = 0

=> 20x + 9 = 0

=> 20x = -9

=> x = -9/20