# Need a strategy for inverting a function

1. Sep 27, 2007

### MCarroll

I can't solve for y from:

x = - $$K_{1}$$* y *$$\sqrt{K_{2}-y}$$

where K(1) and K(2) are constants.

I am pretty sure as a younger man I was taught how to do this but I can't remember the strategies I can/should use. Any thougths would be very appreciated.

Last edited: Sep 27, 2007
2. Sep 27, 2007

### genneth

Square both sides and you get a cubic in y, out of which the solution y=0 is evident, so you've only got a simple quadratic to solve.

3. Sep 27, 2007

### Shooting Star

4. Sep 27, 2007

### genneth

5. Sep 27, 2007

### MCarroll

Thanks, and genneth I'm not one to talk!

Shooting Star, It looks from the page you sent that the general form is:

y = 3f/[-e+(e3-27f2)1/3],
y = 3f/[-e+(e3-27f2)1/3(-1+sqrt[-3])/2],
y = 3f/[-e+(e3-27f2)1/3(-1-sqrt[-3])/2].

so only the first of these avoids i, right?