# How do you find the product of (d-7)(d+7)?

Dec 23, 2016

${d}^{2} - 49$

#### Explanation:

It helps if you can learn to recognise that these are the factors for:

${d}^{2} - 49$, known as the difference between two squares.

If you do not recognise them, so can just multiply out the brackets.
Each term in the first bracket multiplies by each term in the second bracket to get 4 terms.

$\left(d - 7\right) \left(d + 7\right) = {d}^{2} + 7 d - 7 d - 49$

Simplify to get

${d}^{2} - 49$