The Student Room Group

Complex numbers loci

The complex number 1+2i is denoted by u. The complex number v is such that |v|= 2|u| and arg v =arg u+ pi/3.
Sketch on Argand diagram showing the points representing u and v.
So i plotted u=(1,2) in the first quadrant and v=(-2.5,3.8) in the second quadrant.
Is this correct?
Original post by Shas72
The complex number 1+2i is denoted by u. The complex number v is such that |v|= 2|u| and arg v =arg u+ pi/3.
Sketch on Argand diagram showing the points representing u and v.
So i plotted u=(1,2) in the first quadrant and v=(-2.5,3.8) in the second quadrant.
Is this correct?


I got 3.7 (2sig.fig.) for the second coordinate, but it only asks for a sketch, so that's fine.

Edit: I'd mark in the angle pi/3, and the length 252\sqrt 5 for good measure.
(edited 3 years ago)
Reply 2
Original post by ghostwalker
I got 3.7 (2sig.fig.) for the second coordinate, but it only asks for a sketch, so that's fine.

Edit: I'd mark in the angle pi/3, and the length 252\sqrt 5 for good measure.

Thanks a lottt! Can you also pls help me with one more question.16031181679525825897611021386463.jpg
Its the continuation of the same question. I got w=1/2+(sqroot 3)/2 i
How do i explain why v can be expressed a 2uw?
Original post by Shas72
Thanks a lottt! Can you also pls help me with one more question.16031181679525825897611021386463.jpg
Its the continuation of the same question. I got w=1/2+(sqroot 3)/2 i
How do i explain why v can be expressed a 2uw?


Consider the different ways to represent complex numbers, and think about how you get to v from u, in particular at the very start of the question.
Reply 4
Original post by ghostwalker
Consider the different ways to represent complex numbers, and think about how you get to v from u, in particular at the very start of the question.

Yeah i understood. I got 2uw= 1-2sqroot(3)+i[2+sqroot (3)] which is equal to -2.5 +3.7 i=v
Reply 5
Original post by ghostwalker
Consider the different ways to represent complex numbers, and think about how you get to v from u, in particular at the very start of the question.

So v= -2.5+ 3.7 i
Reply 6
Original post by ghostwalker
Consider the different ways to represent complex numbers, and think about how you get to v from u, in particular at the very start of the question.

Thank you so much!!!
Reply 7
Original post by Shas72
So v= -2.5+ 3.7 i

Doesn't the question ask for exact values for a and b, i.e. you leave the square roots (surds) in the answer?
Reply 8
Original post by davros
Doesn't the question ask for exact values for a and b, i.e. you leave the square roots (surds) in the answer?

Thank you so much.
But the ans in the mark scheme is correct of what I have mentioned.
Reply 9
Original post by Shas72
Thank you so much.
But the ans in the mark scheme is correct of what I have mentioned.

No problem - I think I was looking at the image for your subsequent problem where it did ask for exact values :smile:
Reply 10
thank you!

Quick Reply

Latest