Question

Bài 1: Cho đa thức: A = 4x² - 5xy + 3y²;

B = 3x² + 2xy - y²

Tính A + B; A - B

Bài 2: Tìm đa thức M, N biết:

a) M + (5x² - 2xy) = 6x² + 9xy - y²

b) (3xy - 4y²) - N = x² - 7xy + 8y²

Bài 3: Cho đa thức

A(x) = 3x⁴ - \(\dfrac{3}{4}\)x³ + 2x² - 3

B(x) = 8x⁴ + \(\dfrac{1}{5}\)x³ - 9x + \(\dfrac{2}{5}\)

Tính: A(x) + B(x);

A(x) - B(x);

B(x) - A(x)

Answer 1

Bài 1 :

A + B = 4x² - 5xy + 3y² + 3x² + 2xy - y²

= ( 4x² + 3x² ) - ( 5xy - 2xy ) + ( 3y² - y² )

= 7x² - 3xy + 2y²

A - B = 4x² - 5xy + 3y² - ( 3x² + 2xy - y² )

= 4x² - 5xy + 3y² - 3x² - 2xy + y²

= ( 4x² - 3x² ) - ( 5xy + 2xy ) + ( 3y² + y² )

= x² - 7xy + 4y²

Bài 2 :

a) M + (5x² - 2xy) = 6x² + 9xy - y²

M = 6x² + 9xy - y² - (5x² - 2xy)

M = 6x² + 9xy - y² - 5x² + 2xy

M = ( 6x² - 5x² ) + ( 9xy + 2xy ) - y²

M = x² + 11xy - y²

Vậy M = x² + 11xy - y²

b) (3xy - 4y²) - N = x² - 7xy + 8y²

N = 3xy - 4y² - x² - 7xy + 8y²

N = ( 3xy - 7xy ) - ( 4y² - 8y² ) - x²

N = -4xy + 4y² - x²

Vậy N = -4xy + 4y² - x²

Answer 2

3, Cho đa thức

A(x)+B(x) = (3x⁴-\(\dfrac{3}{4}\)x³+2x²-3)+(8x⁴+\(\dfrac{1}{5}\)x³-9x+\(\dfrac{2}{5}\))

= 3x⁴-\(\dfrac{3}{4}\)x³+2x²-3+8x⁴+\(\dfrac{1}{5}\)x³-9x+\(\dfrac{2}{5}\)

= (3x⁴+8x⁴⁾+(-3/4x³+1/5x³)+(-3+2/5)+2x²-9x

= 11x⁴ -0.55x³-2.6+2x²-9x

A(x)-B(x)=(3x⁴-\(\dfrac{3}{4}\)x³+2x²-3)-(8x⁴+\(\dfrac{1}{5}\)x³-9x+\(\dfrac{2}{5}\))

= 3x⁴-\(\dfrac{3}{4}\)x³+2x²-3-8x⁴-\(\dfrac{1}{5}\)x³+9x-\(\dfrac{2}{5}\)

= (3x⁴-8x⁴⁾+(-3/4x³-1/5x³)+(-3-2/5)+2x²+9x

= -5x⁴-0.95x³-3.4+2x²+9x

B(x)-A(x)=(8x⁴+\(\dfrac{1}{5}\)x³-9x+\(\dfrac{2}{5}\))-(3x⁴-\(\dfrac{3}{4}\)x³+2x²-3)

=8x⁴+\(\dfrac{1}{5}\)x³-9x+\(\dfrac{2}{5}\)-3x⁴+\(\dfrac{3}{4}\)x³-2x²+3

=(8x⁴-3x⁴)+(1/5x³+3/4x³)+(2/5+3)-9x-2x²

⁼ 5x⁴+0.95x³+2.6-9x-2x²

Answer 3

còn bài 1 và 2 thì có bn gì đó giải rùi ! Mình không giải nx nha<<,,,,,<<<<<<<<