How is multiplying complex numbers different
from adding or subtracting complex numbers?

Let P and Q be two complex numbers such that

P = a+bi

Q = c+di

Where a,b,c,d are real numbers and i = sqrt(-1).

This means i^2 = -1.

Adding P and Q means

P+Q = (a+bi)+(c+di)

P+Q = a+bi + c+di

P+Q = (a+c) + (bi+di)

P+Q = (a+c) + (b+d)i

As you can see, we just add the corresponding components together.

Subtraction is a similar story.

P-Q = (a+bi)-(c+di)

P-Q = a+bi - c-di

P-Q = (a-c) + (bi-di)

P-Q = (a-c) + (b-d)i

We subtract the corresponding components

Multiplication is a bit more complicated.

We'll use the FOIL rule

P*Q = (a+bi)*(c+di)

P*Q = a*c + a*di + bi*c + bi*di

P*Q = a*c + ad*i + bc*i + bd*i^2

P*Q = a*c + ad*i + bc*i + bd*(-1)

P*Q = a*c + ad*i + bc*i - bd

P*Q = (ac - bd) + (ad*i + bc*i)

P*Q = (ac - bd) + (ad + bc)i

Unfortunately multiplication isn't as simple as addition or subtraction, but we can at least make a tidy formula for it. You could also use the box method to visually organize the terms into a table to help multiply out P and Q.

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step-by-step explanation:

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step-by-step explanation: