Can someone tell me the answer to this and how they got it?

Question

I need to know the answer to this question, but further more I would like to know how you went about getting that answer. Thanks!


(Complex Numbers)
1. For i = , if 3i (2 + 5i) = x + 6i, then x = ?
A. –15
B. 5
C. 5i
D. 15i
E. 27i

Answer 1

Distribute the 3i on the left
3i (2 + 5i) = x + 6i
6i + 15i^2 = x + 6i
Remember that i^2 = -1, so
6i + (15)(-1) = x + 6i
6i - 15 = x + 6i
Now subtract 6i from both sides
-15 = x
So the answer must be "A"

Answer 2

this is easy. step one . 3i x 2 = 6i , and 3i x 5i = -15 because i x i = -1 so u get 6i - 15 = x + 6i . subtract 6i from both side , you get x= -15.

u just need to know (i x i = -1)

Answer 3

3i (2+5i) = x + 6i

1. Subtract 6i from each side: 3i (2+5i) -6i = x

2. Multiply out the parentheses: 3i x 2= 6i and 3i x 5i= 15i, so you have
6i + 15i - 6i = x

3. Adding and subracting all the i's gets 15i = x

Answer 4

A. -15

3i (2 + 5i) = x + 6i
6i + 15(i * i) = x + 6i
6i - 15 = x + 6i
-15 = x