## Identities in complex number

Complex numbers, rational functions, logarithms, sequences and series, matrix operations, etc.

### Identities in complex number

I am confusing about can i use "Identities" in Complex number term!

For example, i have a Complex Conjugate in multiplication : (2 - 4i)(2 + 4i)
And the answer is 20 if i multiply these two parentheses together. But if i use "identity" (a - b)(a + b) = (a - b)^2 , the answers in two different ways were not same!
honest_denverco09

Posts: 52
Joined: Tue Mar 31, 2009 2:06 am

### Re: Identities in complex number

honest_denverco09 wrote:... But if i use "identity" (a - b)(a + b) = (a - b)^2 , the answers in two different ways were not same!

$(a-b)(a+b)=a^2-b^2$

Martingale

Posts: 363
Joined: Mon Mar 30, 2009 1:30 pm
Location: USA

honest_denverco09 wrote:I am confusing about can i use "Identities" in Complex number term!

For example, i have a Complex Conjugate in multiplication : (2 - 4i)(2 + 4i)
And the answer is 20 if i multiply these two parentheses together. But if i use "identity" (a - b)(a + b) = (a - b)^2 , the answers in two different ways were not same!

Please show your steps, displaying what you did that did not arrive that the correct value.

Thank you!

stapel_eliz

Posts: 1804
Joined: Mon Dec 08, 2008 4:22 pm

### Re: Identities in complex number

just square both terms individually so the identity reads:

(a - b)(a + b) = (a^2 - b^2)

if you still get it wrong, check your math because that is the only problem i could find.
supersterfi

Posts: 1
Joined: Sun Apr 12, 2009 9:16 pm