Question

1) Phân tích đa thức thành nhân tử :

a) 25(x+2y)²-16(2x-y)²

b) 0,25(x-2y)²-4(x+y)²

c) \(\dfrac{4}{9}\)(x-3y)²-0,04(x+y)²

d) -25x²+30x-9

2) Tính giá trị biểu thức:

a) 12xy-5y-20x-3y² tại x=-1, y=1

b) -x²+5x-2xy+10y tai x=2, y=1

Answer 1

Câu 1: 

a: \(=\left(5x+10y\right)^2-\left(8x-4y\right)^2\)

\(=\left(5x+10y-8x+4y\right)\left(5x+10y+8x-4y\right)\)

\(=\left(-3x+14y\right)\left(13x+6y\right)\)

b: \(=\left(0.5x-y\right)^2-\left(2x+2y\right)^2\)

\(=\left(0.5x-y-2x-2y\right)\left(0.5x-y+2x+2y\right)\)

\(=\left(-1.5y-3y\right)\left(2.5x+y\right)\)

c: \(=\left(\dfrac{2}{3}x-2y\right)^2-\left(0.2x+0.2y\right)^2\)

\(=\left(\dfrac{2}{3}x-2y-\dfrac{1}{5}x-\dfrac{1}{5}y\right)\left(\dfrac{2}{3}x+2y+\dfrac{1}{5}y+\dfrac{1}{5}x\right)\)

\(=\left(\dfrac{7}{15}x-\dfrac{11}{5}y\right)\left(\dfrac{13}{15}x+\dfrac{11}{5}y\right)\)

d: \(=-\left(5x-3\right)^2\)