Target Exam

CUET

Subject

Section B1

Chapter

Vectors

Question:

The value of $\alpha$ if the angle between $\vec{p}=2\alpha^2\hat{i}-3\alpha\hat{j}+\hat{k}$ and $\vec{q}=\hat{i}+\hat{j}+\alpha\hat{k}$ is obtuse, is

Options:

$R - [0, 1]$

$(0, 1)$

$[0, \infty)$

$[1, \infty)$

Correct Answer:

$(0, 1)$

Explanation:

The correct answer is Option (2) → $(0, 1)$ ##

For obtuse angle, $\cos \theta < 0 \Rightarrow \vec{p} \cdot \vec{q} < 0$

$2\alpha^2 - 3\alpha + \alpha < 0 \Rightarrow 2\alpha^2 - 2\alpha < 0 \Rightarrow \alpha \in (0, 1)$