solve this one.

head - 1
tails - 2

CASES..
HHH or 111 here D<0 so imaginary roots
HHT or 112 here D<0
HTH or 121 here D=0
HTT or 122 here D<0
THH or 211 here D<0
THT or 212 here D<0
TTH or 221 here D<0
TTT or 222 here D<0

Now probability of HTH = 1/8..

So probablity of imaginary roots = 1-1/8 = 7/8?

you've taken H-2 and T-1 ???

edited that : but still same answer ?