Question

How do you multiply `(2-i)(1+7i)` in trigonometric form?

Answer 1

simplify your equation and then use the following formulae: `z=a+bi=|z|(cosθ+isinθ)` and `|z| = sqrt(a^2 + b^2)`

Explanation:

After factoring out your function `(2-i)(1+7i)` you will get `2 + 13i - 7i^2`. Since `i^2 = -1` we get `2 + 13i + 7`. Then we get `9 + 13i = z`. `a=9` and `b=13`. You should be able to do the calculations from there. Good luck.