CUET Preparation Today
If $(\vec{a}-\vec{b}) \cdot(\vec{a}+\vec{b})=27$ and $|\vec{a}|=2|\vec{b}|$, then $|\vec{b}|$ is: |
3 2 $\frac{5}{6}$ 6 |
3 |
The correct answer is Option (1) → 3 $(\vec{a}-\vec{b}) \cdot(\vec{a}+\vec{b})=27$ so $|\vec a|^2-|\vec b|^2=27$ $=4|\vec b|^2-|\vec b|^2=27$ (∵ $|\vec a|=2|\vec b|$) $3|\vec b|^2=27$ $|\vec b|=3$ |
