Bài 2:
a) (4x - 3)(2 - x²) - 2(x - 3)² - 7x³
= 8x - 4x³ - 6 + 3x² - 2x² + 12x - 18 - 7x³
= (-4x³ - 7x³) + (3x² - 2x²) + (8x + 12x) + (-6 - 18)
= -11x³ + x² + 20x - 24
b) B = (x + 3)² - (x - 3)² - (2x - 3)(2 - 5x)
= x² + 6x + 9 - x² + 6x - 9 - 4x + 10x² + 6 - 15x
= (x² - x² + 10x²) + (6x + 6x - 4x - 15x) + (9 - 9 + 6)
= 10x² - 9x + 6
c) C = (x + 1)³ - (x - 1)³ - (1 - 2x)(4x² + 2x + 1)
= x³ + 3x² + 3x + 1 - x³ + 3x² - 3x + 1 - 1 + 8x³
= (x³ - x³ + 8x³) + (3x² + 3x²) + (3x - 3x) + (1 + 1 - 1)
= 8x³ + 6x² + 1
Bài 3
a) A = (2x - 1)² - 2(2x - 1)(2x + 3) + (2x + 3)²
= (2x - 1 - 2x - 3)²
= (-4)²
= 16
Vậy A = 16
b) B = x² + 4y²
= x² + 4xy + 4y² - 4xy
= (x + 2y)² - 4xy
= 5² - 4.(-2)
= 25 + 8
= 33
Vậy B = 33
3:
a: \(A=\left(2x-1\right)^2-2\left(2x-1\right)\left(2x+3\right)+\left(2x+3\right)^2\)
\(=\left(2x-1-2x-3\right)^2\)
\(=\left(-4\right)^2=16\)
Do đó: A không phụ thuộc vào biến x
Vậy: Khi x=99 thì A=16
d: \(D=x^2+4y^2=x^2+4xy+4y^2-4xy\)
\(=\left(x+2y\right)^2-4xy\)
\(=5^2-4\cdot\left(-2\right)=25+8=33\)
