Question

(X+5)(x-5)

Answer 1

`(x+5)(x-5) = x^2 - 5^2 = x^2 - 25`

Áp dụng HĐT `(a-b)(a+b) = a^2 - b^2`

Answer 2

\(=x^2-25\)

ADHĐT : \(\left(a^2-b^2\right)=\left(a-b\right)\left(a+b\right)\)

Answer 3

\(\left(x+5\right)\left(x-5\right)\)

\(\Leftrightarrow x\left(x-5\right)+5\left(x-5\right)\)

\(\Leftrightarrow x^2-5x+5\left(x-5\right)\)

\(\Leftrightarrow x^2-5x+5x-25\)

\(\Leftrightarrow x^2-25\)