So I'm following along in my book where it comes to put the final values in the equation:

cosO=u*v/|u|*|v|

= -1/sqrt 6 (5)

and I should get -0.14 But I'm not getting it?

am I inputting it into the calculator the wrong way?

I use cos^-1(-1/sqrt 6 (5)) but I get 1.85 and not -0.14