Fit[{{-1, 1}, {1, 2}, {3, 4}, {5, 6}}, {1, x, x^2, x^3, x^4}, x]

Uh oh! Wolfram|Alpha doesn't run without JavaScript.

Please enable JavaScript. If you don't know how, you can find instructionshere.Once you've done that, refresh this page to start using Wolfram|Alpha.