I have the following vectors and
To find the area of the triangle I used the dot product between these vectors to get the angle and then applied the formula to find the area of the triangle which gave me 15.07(2dp).
However in the given solutions the answer is given as
I think they have used the trig identity to find the value of rather than to find the angle ACB. However I don't understand why there would be such a discrepancy between the two answers; one using and the other using the trig identity.