# Math Help - quick complex number qu.

1. ## quick complex number qu.

if i want to find the complex number of say:

|z|=3 rt(7) and Re(z)=0 ....point of intersection

then id get to y^2= 3 rt(7) and would i take the negative root and just make into a complex number so 3rt(7) i
??

2. Originally Posted by skystar
if i want to find the complex number of say:

|z|=3 rt(7) and Re(z)=0 ....point of intersection

then id get to y^2= 3 rt(7) and would i take the negative root and just make into a complex number so 3rt(7) i
??
Geometrically it is seen that $|z|=3 \sqrt{7}$ is a circle of radius $3 \sqrt{7}$ with centre at the origin. Re(z) = 0 is the imaginary axis. Clearly then the points of intersection are $(0, 3 \sqrt{7})$ and $(0, - 3 \sqrt{7})$.

By the way, $|iy| = 3 \sqrt{7} \Rightarrow |i| |y| = 3 \sqrt{7} \Rightarrow |y| = 3 \sqrt{7} \Rightarrow y = \pm 3 \sqrt{7}$.

Again, you've misunderstood how to get the magnitude of a complex number.