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Need solution for RD Sharma Maths Class 12 Chapter 26 Directions Cosines and Direction Ratios Exercise Very Short Answer Question, question 6.

Answers (1)

Answer:

13 units

Hint:

d=\sqrt{\left(x_{1}-x_{2}\right)^{2}+\left(y_{1}-y_{2}\right)^{2}+\left(z_{1}-z_{2}\right)^{2}}

Given:

P(3, -5, 12 )

Solution:

The direction cosines of x-axis is b_1 (1, 0, 0)

Let A(\lambda, 0,0) be the point on x-axis.

From P(3, -5, 12 ) drawn a line on x-axis perpendicularly in x-axis at A(\lambda, 0,0).

Distance of cosines of AP=b_2\left ( 3-\lambda ,-5, 12 \right )

we know that 

\begin{aligned} &\overrightarrow{b_{1}} \cdot \overrightarrow{b_{2}}=0 \\ &\Rightarrow 1 \times(3-\lambda)=0 \\ &\Rightarrow 3-\lambda=0 \\ &\Rightarrow \lambda=3 \\ &\therefore A=(3,0,0) \\ &A P=\sqrt{(3-3)^{2}+(0+5)^{2}+(12-0)^{2}} \\ &=\sqrt{25+144} \\ &=\sqrt{169} \\ &=13 \end{aligned}

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