(-2, 5, -6)^{T} **·** ( 1, 2, 3)^{T} =
(-2)*1 + 5*2 + (-6)*3 = -2 + 10 -18 = -10

The answer is a negative real. This is fine. Dot products produce all kinds of reals: negative, zero, positive. However, something interesting happens when you take the dot product of a vector with itself.

What is:

(1, -3)^{T}·(1, -3)^{T}= ?