8 a + 4 b + 2 c + d = 0 , -8 a + 4 b - 2 c + d = 56 , 12 a - 4 b + c = 0 , 27 a + 6 b + c = 0

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.