JEE PYQ: Vector Algebra Question 18
Question 18 - 2020 (03 Sep Shift 2)
Let $a, b, c \in \mathbb{R}$ be such that $a^2 + b^2 + c^2 = 1$. If $a\cos\theta - b\cos\left(\theta + \frac{2\pi}{3}\right) = c\cos\left(\theta + \frac{4\pi}{3}\right)$, where $\theta = \frac{\pi}{9}$, then the angle between the vectors $a\hat{i} + b\hat{j} + c\hat{k}$ and $b\hat{i} + c\hat{j} + a\hat{k}$ is:
(1) $\frac{\pi}{2}$
(2) $\frac{2\pi}{3}$
(3) $\frac{\pi}{9}$
(4) $0$