FP3 - Vectors

The formula is: $\boldsymbol{a} \cdot \mathbf{b}=(a_{1},a_{2},a_{3}) \cdot (b_{1},b_{2},b_{3})=a_{1}b_{1}+a_{2}b_{2}+a_{3}b_{3}$

This is exactly what has happened in part a. So I'm not sure what you mean by it doesn't follow the formula?

Do you mean it doesn't follow: $\boldsymbol{a}\cdot \mathbf{b}=|\boldsymbol{a}|| \boldsymbol{b} |cos\Theta$
?

Yes that's what I meant. It didn't follow the second formula. Am I correct in presuming, that if an angle has not been indicated I use

And when an angle is indicated I use


Sorry this may sound stupid it's just vectors are my least favorite topic in maths!