• Support PF! Buy your school textbooks, materials and every day products Here!

Expressing as complex numbers

  • Thread starter Ry122
  • Start date
565
2
How do I express the following in the form a+ib?

[tex] (\sqrt{-4} - 1) (\sqrt{-9}) [/tex]

My attempt:
(2i - 1)(3i)
6i-3i = 3i
 
Last edited:

Answers and Replies

StatusX
Homework Helper
2,563
1
Close, but (2i)(3i)=6i2=-6, not 6i.
 
565
2
Can you tell me why the answer -6-+3i has plus or minus 3i?

Also can you tell me the answer to (3+i)^2 - (3+i)^2
The answer I got was 0.
9+6i+i^2-9-6i-i^2=0
 
Last edited:
Dick
Science Advisor
Homework Helper
26,258
618
You have to define what you mean by sqrt(-n) for n>0. You could choose it to be either i*sqrt(n) or -i*sqrt(n). That's your sign ambiguity.
 
HallsofIvy
Science Advisor
Homework Helper
41,738
897
Can you tell me why the answer -6-+3i has plus or minus 3i?
What was that the answer to?? Surely not the (2i-1)(3i) problem you were just talking about!

Also can you tell me the answer to (3+i)^2 - (3+i)^2
The answer I got was 0.
9+6i+i^2-9-6i-i^2=0
The answer to a2- a2 is 0 no matter what a is!
 

Related Threads for: Expressing as complex numbers

  • Last Post
Replies
7
Views
2K
Replies
2
Views
19K
Replies
2
Views
711
Replies
1
Views
3K
Replies
2
Views
5K
Replies
7
Views
2K
Replies
6
Views
2K
Top