The solution of complex number (1 Viewer)

[Richard Lee]

(x+iy)^2=3-4i=(2-i)^2
Therefore:
x+iy=(+/-) (2-i)

 

[Rahul]

should we be looking for this in every situation?
or doing it the other way(equating real/img parts)?

 

[felix_js]

you could do this:

x+y = 5 (from the modulus) -(1)
x-y =3 (getting the reals) -(2)

2x=8
x=4

2y=2
y=1

 

[ND]

Yeh there's no point expanding and equating, just think about it in your head.

 

[Richard Lee]

How long can u work this question out?
No point, but works!
What r u looking for? Not the right solution!

 

[maniacguy]

Richard - you don't have a *method* there.
Being able to spot the square roots is fine for small numbers, but tell me, if I ask you to find the square root of, say,
1029340345 + 234235382912i

How do you plan on going about this?

 

[freaking_out]

Originally posted by maniacguy
...if I ask you to find the square root of, say,
1029340345 + 234235382912i

 

[Newbie]

i dont get the original post?
was that suppose to help us somehow?

 

[freaking_out]

Originally posted by Newbie
i dont get the original post?
was that suppose to help us somehow?

i guess so, since its titled "the solution...".

 

[McLake]

Deciding if I should delete ...

 

[freaking_out]

Originally posted by McLake
Deciding if I should delete ...

lol. don't worry, i've seen worst posts.

 

[underthesun]

Originally posted by maniacguy
Richard - you don't have a *method* there.
Being able to spot the square roots is fine for small numbers, but tell me, if I ask you to find the square root of, say,
1029340345 + 234235382912i

How do you plan on going about this?

De_moivre's_theorem ?

 

[freaking_out]

Originally posted by underthesun
De_moivre's_theorem ?

zis, preblem, is noth saposed 2 b worked out.

 

[maniacguy]

I was commenting on the fact that Richard's apparent method was simply solving by inspection. That's insane for large numbers, human calculators excluded.

 

[Richard Lee]

Originally posted by maniacguy
Richard - you don't have a *method* there.
Being able to spot the square roots is fine for small numbers, but tell me, if I ask you to find the square root of, say,
1029340345 + 234235382912i

How do you plan on going about this?

Good question!
If u got this question in HSC. Just forgot it and don't waste u time!

 

[turtle_2468]

 

[ND]

Originally posted by Richard Lee
Good question!
If u got this question in HSC. Just forgot it and don't waste u time!

Forget it? That's just throwing away easy marks. It doesn't take long to expand (x+iy)^2 and equate.

 

[freaking_out]

Originally posted by ND
Forget it? That's just throwing away easy marks. It doesn't take long to expand (x+iy)^2 and equate.

yeah, true that, coz these days we have calculators.

 

[maniacguy]

*chuckle* Those numbers aren't going to work on a calculator - too big to be accurate.

But my point was that it's not always obvious what the factorization is straightaway, especially if surds are involved. (Although I like Richard's response to the example - those numbers are big enough that you're better off skipping the question at first)

More to the point, in the HSC you would lose marks if you didn't put any working down. It's easier to just write the thing out.