Question

1. Rút gọn:

(a +2 )² - (a + 2) (a - 2)

2. Tìm x

a) (2x + 3)² - 4(x - 1) (x + 1) = 49

b) 16x² - (4x - 5)² = 15

3. Tính giá trị của biểu thức:

P= (x + 3)² + (x - 3) (x + 3) - 2(x + 2) (x - 4) với x = \(\frac{-1}{2}\)

Answer 1

1.\(\left(a+2\right)^2-\left(a+2\right)\left(a-2\right)\)

\(=a^2+4a+4-a^2+4\)

\(=4a+8\)

\(2.a,\left(2x+3\right)^2-4\left(x-1\right)\left(x+1\right)=49\)

\(\Leftrightarrow4x^2+12x+9-4x^2+4-49=0\)

\(\Leftrightarrow12x-36=0\)

\(\Leftrightarrow x=3\)

\(b,16x^2-\left(4x-5\right)^2=15\)

\(\Leftrightarrow16x^2-16x^2+40x-25=15\)

\(\Leftrightarrow x=1\)

\(3.P=\left(x+3\right)^2+\left(x+3\right)\left(x-3\right)-2\left(x+2\right)\left(x-4\right)\)

\(=x^2+6x+9+x^2-9-2\left(x^2-2x-8\right)\)

\(=2x^2+6x-2x^2+4x+16\)

\(=10x+16\)

Thay x \(=-\frac{1}{2}\) vào P:

\(P=10.\frac{-1}{2}+16=11\)