## Precalculus: Mathematics for Calculus, 7th Edition

$(3-7i)(3+7i) = 58$
1. $(3-7i)(3+7i)$ 2.Use the difference of two squares formula $a2−b2=(a+b)(a−b)$ (or Multiply the two binomials together (use the FOIL method to distribute the First, Outer, Inner, and Last terms)): $9-49i^{2}$ 3. Change $-49i^{2}$ to 49, because $i^{2} = -1$ and $-49\times-1 = 49$:$9+49$ 4. Add the two numbers together: 58