Question

Perform the indicated operations. Write the answer in standard form, a+bi.
(9 + 2i)(9 - 2i)

Answer 1

Answer:

It can't be expressed in that form

Step-by-step explanation:

From difference of two squares:

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

a » 9

b » 2i

$(9 + 2i)(9 - 2i) = \{ {(9)}^{2} - {(2i)}^{2} \} \\ \\ = (81 - 4 {i}^{2} )$

but i² is -1 [ complex numbers ]

$= \{81 - 4( - 1) \} \\ = 81 + 4 \\ = 85$

Answer 2

Answer:

$(9 + 2i)(9 - 2i) \: \\ this \: can \: be \: wrtten \: as \: \\ {9}^{2} - {2i}^{2} = 81 - 4 \times - 1 \\ = 81 + 4 = 85 \\ then \: 85 + 0i \\ thank \: you$