Question

Rút gọn :

D= \(\left(x+7\right)^2-\left(x-7\right)^2\)

Answer 1

=(x+7+x-7).(x+7-x+7)=2x.14=28x

Answer 2

\(D=\left(x-7\right)^2-\left(x-7\right)^2\)

\(=\left(x+7+x-7\right)\left(x+7-x+7\right)\)

\(=2x.14\)

\(=28x\)

Answer 3

D= (x+7)² - (x-7)²

D= (x+7-x+7).(x+7+x-7)

D= 14.2x

D=28x

Answer 4

\(\left(x+7\right)^2-\left(x-7\right)^2\)

D=\([\left(x+7\right)+\left(x-7\right)]\left[\left(x+7\right)-\left(x-7\right)\right]\)

D=\(\left(x+7+x-7\right)\left(x+7-x+7\right)\)

D=\(2x\)\(\times\)14=28x