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# Complex numbers watch

1. Question is:
12 = [(47+j100) ((10-j25i2) / j100)] + j100i2

Im stuck on the part:
((10-j25i2) / j100)

Any help?

Do I need to first look at it as:
10/j100 - j25i2/j100
2. I need to explain this better, basically i need to find out:

(10 - j25) / j100
3. Not sure what you mean by the subscript i2?
4. (Original post by doodlelizzie)
Not sure what you mean by the subscript i2?
I know by me putting in the subscript it confuses the situation without knowing the whole question, so thats why I replied again saying only:

(10 - j25) / j100

So I was asking do I approach it as:

(10 / j100) - (j25 / j100)

So then could I say:

j0.1 - j0.25 ??????

Im doing complex numbers but this is the 1st time I came across this setup
5. All you have to do is multiply the numerator and denominator by -j

6. (Original post by picklesmartyn)
I know by me putting in the subscript it confuses the situation without knowing the whole question, so thats why I replied again saying only:

(10 - j25) / j100

So I was asking do I approach it as:

(10 / j100) - (j25 / j100)

So then could I say:

j0.1 - j0.25 ??????

Im doing complex numbers but this is the 1st time I came across this setup
Can you remember in GCSE when to simplify expression such as you had to multiply top and bottom by ? You just have to do the same thing here, but with j rather than .
7. (Original post by jsMath)
All you have to do is multiply the numerator and denominator by -j

so that it then becomes:

- j10 - 25 / 100

which is then:

0.25 - j0.1 ???????
8. (Original post by brittanna)
Can you remember in GCSE when to simplify expression such as you had to multiply top and bottom by ? You just have to do the same thing here, but with j rather than .
I do remember some simplifying fractions work, Ive just been out the subject for a while
9. I know that when you get a scenario like:

3+2i / 4-3i

you multiply he numerator and denominator by the conjugate of the denominator:

(3+2i / 4-3i) x (4+3i / 4+3i)

But nowhere can I find an example like the one above where there is a single denominator that is a complex number aswell. Maybe im looking to hard into it!!
10. (Original post by picklesmartyn)
I know that when you get a scenario like:

3+2i / 4-3i

you multiply he numerator and denominator by the conjugate of the denominator:

(3+2i / 4-3i) x (4+3i / 4+3i)

But nowhere can I find an example like the one above where there is a single denominator that is a complex number aswell. Maybe im looking to hard into it!!
It's the same idea but the real part is zero - so you are multiplying by the complex conjugate.
11. (Original post by picklesmartyn)
so that it then becomes:

- j10 - 25 / 100

which is then:

0.25 - j0.1 ???????
You were asking to simplify the above expression, then yes that would be the answer, if you were asked something else then kindly let us know

You need to ask the right question in order to get the right answer,

In general the idea is to get rid of the j in the den...
12. (Original post by Muttley79)
It's the same idea but the real part is zero - so you are multiplying by the complex conjugate.
oh right so what your saying is:

10 - j25 / j100

is the same as:

10 - j25 / 0 + j100

so the conjugate is:

0 - j100 ??????
13. (Original post by picklesmartyn)
so that it then becomes:

- j10 - 25 / 100

which is then:

0.25 - j0.1 ???????
then you can multiply it by 100
14. (Original post by picklesmartyn)
oh right so what your saying is:

10 - j25 / j100

is the same as:

10 - j25 / 0 + j100

so the conjugate is:

0 - j100 ??????
Yes
15. (Original post by Muttley79)
Yes
Oh my god I knew it was something simple i forgot about the real part with respect to the imaginary part

Thanks everyone
16. (Original post by picklesmartyn)
Oh my god I knew it was something simple i forgot about the real part with respect to the imaginary part

Thanks everyone
Don't worry - it's easy to overlook

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Updated: September 8, 2015
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