JEE MAIN - Mathematics (2024 - 31st January Morning Shift - No. 12)

The distance of the point $$Q(0,2,-2)$$ form the line passing through the point $$P(5,-4, 3)$$ and perpendicular to the lines $$\vec{r}=(-3 \hat{i}+2 \hat{k})+\lambda(2 \hat{i}+3 \hat{j}+5 \hat{k}), \lambda \in \mathbb{R}$$ and $$\vec{r}=(\hat{i}-2 \hat{j}+\hat{k})+\mu(-\hat{i}+3 \hat{j}+2 \hat{k}), \mu \in \mathbb{R}$$ is :
$$\sqrt{74}$$
$$\sqrt{86}$$
$$\sqrt{54}$$
$$\sqrt{20}$$

Explanation

A vector in the direction of the required line can be obtained by cross product of

$$\begin{aligned} & \left|\begin{array}{ccc} \hat{i} & \hat{j} & \hat{k} \\ 2 & 3 & 5 \\ -1 & 3 & 2 \end{array}\right| \\\\ & =-9 \hat{i}-9 \hat{j}+9 \hat{k} \end{aligned}$$

Required line

$$\begin{aligned} & \overrightarrow{\mathrm{r}}=(5 \hat{\mathrm{i}}-4 \hat{\mathrm{j}}+3 \hat{\mathrm{k}})+\lambda^{\prime}(-9 \hat{\mathrm{i}}-9 \hat{\mathrm{j}}+9 \hat{\mathrm{k}}) \\\\ & \overrightarrow{\mathrm{r}}=(5 \hat{\mathrm{i}}-4 \hat{\mathrm{j}}+3 \hat{\mathrm{k}})+\lambda(\hat{\mathrm{i}}+\hat{\mathrm{j}}-\hat{\mathrm{k}}) \end{aligned}$$

Now distance of $$(0,2,-2)$$

JEE Main 2024 (Online) 31st January Morning Shift Mathematics - Vector Algebra Question 41 English Explanation

$$\begin{aligned} & \text { P.V. of } \mathrm{P} \equiv(5+\lambda) \hat{i}+(\lambda-4) \hat{j}+(3-\lambda) \hat{k} \\\\ & \overrightarrow{\mathrm{AP}}=(5+\lambda) \hat{i}+(\lambda-6) \hat{j}+(5-\lambda) \hat{k} \\\\ & \overrightarrow{\mathrm{AP}} \cdot(\hat{\mathrm{i}}+\hat{\mathrm{j}}-\hat{\mathrm{k}})=0 \\\\ & 5+\lambda+\lambda-6-5+\lambda=0 \\\\ & \lambda=2 \\\\ & |\overrightarrow{\mathrm{AP}}|=\sqrt{49+16+9} \\\\ & |\overrightarrow{\mathrm{AP}}|=\sqrt{74} \end{aligned}$$

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