hello to everybody !

could someone shed a light on this please.

the following matrix is given:

now, show that this matrix is indefinite by calculating (x^t)(Ax) with the vektors x^t = (1,1,0,0) and x^t=(0,1,1,0).Code:2, 5, 1, 0 5, 2, -2, 1 1, -2, 1, 0 0, 1, 0, 8

thanks in advance!