When t=-1 the expression=0, so -1 is a zero. Divide by this zero to reduce to a quadratic:
-1 | 1 -2 14 17
1 -1 3 | -17
1 -3 17 | 0 = x2-3x+17.
Now we can find the complex zeroes.
x2-3x=-17,
x2-3x+9/4=-17+9/4=-59/4,
(x-3/2)2=-59/4,
x-3/2=±i√59/2, x=3/2+i√59/2, 3/2-i√59/2.