# A question on limits

1. Oct 25, 2011

### Manni

I need help with this question. I understand that logic behind it; as P approaches O the value the right bisector Q reaches it's maximum. I don't know how to show this algebraically however. Help?

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2. Oct 25, 2011

### micromass

Staff Emeritus
We give P the coordinates (x,y). We know that P is on the parabola, so we know that

$$P=(x,x^2)$$

Now, can you find the coordinates of the point Q??

3. Oct 25, 2011

### Manni

Ok, so the bisector would intersect P at point x/2. Because I know that the x coordinate on Q is 0, how would I find it's y?

4. Oct 25, 2011

### micromass

Staff Emeritus

- Find the midpoint M between 0 en P.
- Find the equation of the line L going through 0 and P
- Find a vector perpendicular to the line L
- Construct the equation of the line R going through M and perpendicular through L
- Find Q as the intersection between R and the y-axis.

All of these questions involve nothing more than 10th grade geometry. So you should be able to complete these easily.

5. Oct 25, 2011

### Manni

How do I show algebraically that Q approaches infinity as P approaches the origin?

6. Oct 26, 2011

### micromass

Staff Emeritus
It doesn't approach infinity.

Did you find the expression for Q?