Math Question

[lightnb]

My other equation isn't working right either...

I have the two variables, and depending on which one the user gives, it should solve for the other. but it seems that the answers don't work the other way:

for example if I set $FA and get an answer for $MFh, then use that answer to solve for $FA again, the answer i get isn't the number I started with.

the two equations are:

PHP Code:

$MFh=2*(tan($FA*$FA)); 


and

PHP Code:

$FA = sqrt(rad2deg(atan($MFh/2))); 


any ideas?