Question:
In a triangle $\mathrm{ABC}$, if $|\overrightarrow{\mathrm{BC}}|=3,|\overrightarrow{\mathrm{CA}}|=5$ and $|\overrightarrow{\mathrm{BA}}|=7$, then the projection of the vector $\overrightarrow{\mathrm{BA}}$ on $\overrightarrow{\mathrm{BC}}$ is equal to
Correct Option: , 3
Solution:
Projection of $\overrightarrow{\mathrm{BA}}$
on $\overrightarrow{\mathrm{BC}}$ is equal to
$=|\mathrm{BA} \overrightarrow{\mathrm{A}}| \cos \angle \mathrm{ABC}$
$=7\left|\frac{7^{2}+3^{2}-5^{2}}{2 \times 7 \times 3}\right|=\frac{11}{2}$