Question

In a triangle $A B C$, if $|\overrightarrow{B C}|=3,|\overrightarrow{C A}|=5$ and $|\overrightarrow{B A}|=7$, then the projection of the vector $\overrightarrow{B A}$ on $\overrightarrow{B C}$ is equal to

• A. $\frac{19}{2}$
• B. $\frac{13}{2}$
• C. $\frac{11}{2}$
• D. $\frac{15}{2}$

Answer 1

Answer: (C)

Projection of $\overrightarrow{B A}$ on $\overrightarrow{B C}$ is equal to
$=|\overrightarrow{B A}| \cos \angle A B C $
$=7\left|\frac{7^{2}+3^{2}-5^{2}}{2 \times 7 \times 3}\right|=\frac{11}{2}$