t=sqrt(s(s-a)(s-b)(s-c)),s=(a+b+c)/2,a=8.9,b=15.2,c=12.7

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.