# Math Help - Complex quadratic equation problem

1. ## Difficult quadratic equation problem

Hi, I have an 'advanced quadratic' problem which I'm not sure how to solve.

Let pairs $(a, c)$ and $(b, d)$ be roots of the equation $x^2 + ax - b = 0$ and $x^2 + cx + d = 0$ respectively. Find all possible real values for $a, b, c, d.$

Thanks for any help, BG

2. Here's a start.

Since (a,c) are the roots of $x^{2}+ax-b$, then we can write it as

$(x-a)(x-c)=x^{2}+ax-b$

For the other, we can write:

$(x-b)(x-d)=x^{2}+cx+d$

Try equating coefficients and see what you come up with.

Some advice. I assume when you wrote 'complex' you meant the problem was difficult. Do not use the word complex unless you are referring to the non-real numbers. It may add confusion. Just a thought.

3. I think we could use Viete's formula:

$x_1 + x_2 = -\frac{b}{a}$

$x_1 \times x_2 = \frac{c}{a}$

So in this case, for equation 1, with $(a, c)$ = $(x_1, x_2)$ we could do: $x_1 + x_2 = -\frac{b}{a}$ and $x_1 \times x_2 = \frac{c}{a}$ and with $(b, d)$ being $(x_3, x_4)$, $x_3 + x_4 = -\frac{b}{a}$ and $x_3 \times x_4 = \frac{c}{a}$

Just a suggestion, I'm not too sure what to try apart from that.