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by **honest_denverco09** on Sat Apr 11, 2009 8:18 pm

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! :confused:

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by **Martingale** on Sat Apr 11, 2009 8:59 pm

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

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

by **stapel_eliz** on Sat Apr 11, 2009 9:01 pm

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!

by **supersterfi** on Sun Apr 12, 2009 9:27 pm

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.

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