Uh oh! Wolfram|Alpha doesn't run without JavaScript.
Please enable JavaScript. If you don't know how, you can find instructions
here
.
Once you've done that, refresh this page to start using Wolfram|Alpha.
9/x = a/b, 4/x = c/d, d + c = b + a, 1/b + 1/a = 1/d + 1/c
Natural Language
Math Input
Extended Keyboard
Examples
Upload
Random