# How do you multiply (7-3i)(7+3i)?

Jul 26, 2016

$58$

#### Explanation:

Note that for any $a , b$ the difference of squares identity holds:

${a}^{2} - {b}^{2} = \left(a - b\right) \left(a + b\right)$

So we find:

$\left(7 - 3 i\right) \left(7 + 3 i\right) = {7}^{2} - {\left(3 i\right)}^{2} = 49 - 9 {i}^{2} = 49 + 9 = 58$