complex num. question (1 Viewer)

[Triage]

I was just going through cambridge ext 2 maths and came across a question.

1-2i is a root of x^2 - (3+i)x + k = 0. find k and the other root of the equation.

Now I got the answer for k to equal 8-i which is correct but then I looked at the question and thought I could've just as easily chosen the negative root from the quadratic formula and got 8+i.

What am I missing?

 

[Carrotsticks]

Quadratic?

To get K, can't you just substitute 1-2i into the quadratic, then let it equal 0?

Also, to get the other root, you can use the sum of roots = 3+i.

So 1-2i + A = 3+i, so A=2+3i (other root).

K can also be found by considering the product of roots.

 

[Triage]

cheers. Just overlooked the obvious.