Question

How do you find the product `(5r+7)(5r-7)`?

Answer 1

`(5r+7)(5r-7)=25r^2-49`

Explanation:

`color (red)((x-a)(x+a)=x^2-a^2)`
`(5r+7)(5r-7)=(5r)^2-(7)^2=25r^2-49`

`"or"`

`(5r+7)(5r-7)=5r*5r-5r*7+7*5r-7*7`

`(5r+7)(5r-7)=25r^2cancel(-35r)cancel(+35r)-49`

`(5r+7)(5r-7)=25r^2-49`