Question

2. If (x + yi) / i = ( 7 + 9i ) , where x and y are real, what is the value of (x + yi)(x - yi)?

Answer 1

Instead you can do the following:
(x + yi) / i = ( 7 + 9i )

So bring the i to the right hands side

x+iy= (7+9i)(i)=-9+7i

So now you know x+iy

Take conjugate of x+iy to find x-iy =?

Then multiply x+iy and x-iy to find your answer

Answer 2

*hand

Answer 3

what about (71 + 9i^2)(7i - 9i^2)

Answer 4

7i + 9i^2 *

Answer 5

@lgbasallote , are you asking me or @kingmana

Answer 6

im suggesting a solution :P

Answer 7

@lgbasallote , xD

Answer 8

since i^2 = -1 it becomes

(7i - 9)(7i + 9)

use that difference of two squares thingy then keep on simplifying as long as you se an i^2 change it to a -1

Answer 9

change it to -1*