0
$\begingroup$

From the figure below enter image description here

It is given that length of BC=3# we are asked to find scalar product of vectors AB$ and $BC$

I don't know methods to solve such problems and please help me.

  • 0
    aa ok see this it is written in georgian language but question is the same as i wrote see it http://www.naec.ge/images/doc/MASC_SERT/2011pedagogebi-matematikai.pdf number 192011-08-16

1 Answers 1

1

If by scalar product, you mean dot product, then the answer would be $-9$. The definition of cosine says $|\vec{BC}|=|\vec{AB}|\cos(\angle ABC)$; note that $cos(\angle ABC)>0$ since it is acute. Since $\vec{BA}\cdot\vec{BC}=|\vec{BC}||\vec{AB}|\cos(\angle ABC)$ and $\vec{AB}=-\vec{BA}$, we get that $\vec{BA}\cdot\vec{BC}=-|\vec{BC}|^2$.

  • 0
    thanks very much @robjohn i have seen everything and got right answer you answer helped very much thanks ones again2011-08-16