Below is the question I have been working with:
And here is the solution:
Now, I’m stuck with part c. I’ve tried searching online but noone seems to be focusing on the problem that keeps me from understanding the solution to this question. Reading the solution to part c, it seems that cosine of theta is eliminated and the absolute value of the vector product of a and b and the absolute value of the vector c are unified into one absolute value. But, how was cosine of theta eliminated?
It probably has to do with the explanation that’s given right before the answer but I totally do not understand what it has to do with transforming the expression from the one including cosine of theta to the one without (ie the answer). I understand what they’re saying but I don’t understand what it has to do with finding the final answer...
(The only method that has led me even close to the correct final answer is by use of the following identity given in my math data booklet (the top one):
But using it results in one over six times the scalar product of the vector product of a and b and the vector c. This lacks the absolute value around the scalar product as given in the printed solution...)