Question

1. khai triển

a) (2 - 3x)²

b) (x - 4) (x + 4)

c) (x - 1)² - (x + 2)²

2.thêm bớt đưa về chứa bình phương

a) A= x² - 14x

b) B= 1/4x² + x

c) C= 4x² + 12x - 1

d) D= 5x² + 3 - 2x

giúp mk với! cảm ơn

Answer 1

1a. \(\left(2-3x\right)^2=4-12x+9x^2=9x^2-12x+4\)

\(b.\left(x-4\right)\left(x+4\right)=x^2-16\)

\(c.\left(x-1\right)^2-\left(x+2\right)^2=\left(x-1+x+2\right)\left(x-1-x-2\right)=\left(2x+1\right)\left(-3\right)=-6x-3\)

2. a) \(A=x^2-14x=x^2-2.7.x+7^2-49=\left(x-7\right)^2-49\)

\(b.B=\dfrac{1}{4}x^2+x=\dfrac{1}{4}\left(x^2+4x\right)=\dfrac{1}{4} \left(x^2+2x.2+2^2-4\right)=\dfrac{1}{4}\left[\left(x+2\right)^2-4\right]=\dfrac{1}{4}\left(x+2\right)^2-1\)

c.d Tương tự