# Derivation of graph of v against u

1. Aug 23, 2014

### desmond iking

1. The problem statement, all variables and given/known data
This is the graph of v against u .
i am having problem of getting the shape of graph and getting the point (2f, 2f) . can anyone teach me how to derive it?

2. Relevant equations

3. The attempt at a solution
sorry. i dont know how to use LATEX. it may be quite untidy if i type it using / sign for all the equation.

so , i have did it beside the graph in the photo . hopefully you guys can understand .

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2. Aug 23, 2014

### Orodruin

Staff Emeritus
The question is a bit unclear. Is this the full problem exactly as stated?

It seems you want to find the point where the curves u=v and 1/u + 1/v = 1/f intersect. What happens if you insert the first relation into the second and solve for v?

3. Aug 23, 2014

### desmond iking

this is not a question actually. it's just a note. Can you explain further? i am actually finding v against u in my working. to get the shape of the graph. unfortunealy, i got stucked.

4. Aug 23, 2014

### haruspex

See if you can get the equation into the form $v - A = \frac B{u-C}$

5. Aug 23, 2014

### desmond iking

thanks , after referring to the old book, i managed to understand it.