2x^2 + 3x + 8x - x^2 + 4x + k has a double root
combine like terms (2x2 – x2) + (3x +8x + 4x) + k
x2 + 11x + k
to have a double root,
i.e., both roots are the same,
the discriminate must equal zero b2 – 4ac = 0
(11)2 – (4)(1)(k) = 0
121 – 4k = 0
–4k = –121
k = 121 / 4
.