# Quadratic Simultaneous Equation

1. Sep 17, 2013

### fonz

1. The problem statement, all variables and given/known data
Solve the equation for x

$y^2 = 4x$

$x^2 = 4y$

2. Relevant equations

None

3. The attempt at a solution

$y^2 -4x = x^2 - 4y = 0$

I have spent ages re-arranging and substituting in values but I just cannot solve this thing.

2. Sep 17, 2013

### CAF123

Why don't you try to rearrange the second equation for y and sub into the first equation. This will give you an equation entirely in terms of x.

3. Sep 24, 2013

### fonz

$y = 2\sqrt{x}$
$y = \frac{x^{2}}{4}$

I still have no idea how to find $x$

4. Sep 24, 2013

### Staff: Mentor

You didn't do what CAF123 suggested, which was to solve for y in the second equation, and then substitute for y in the first equation.

You solved for y in the second equation, but then solved for y (incorrectly) in the first equation. Note that if y2 = 4x, then y = 2√x is only one of two solutions.

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