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Please solve RD Sharma class 12 chapter 28 The Plane exercise Fill in the blank question 17 maths textbook solution

Answers (1)

Answer:

 sin^{-1}\left [ \frac{9}{\sqrt{156}} \right ]

is the angle between the line and the plane

Hint:

 Find \theta using vector dot product

Given:

 \vec{r}=\left ( 5\hat{i}-\hat{j}-4\hat{k} \right )+\lambda \left ( 2\hat{i}-\hat{j}-\hat{k} \right ) \text { and the plane }\vec{r}. \left ( 3\hat{i}-4\hat{j}-\hat{k} \right )+5=0

Solution:

Line

\vec{r}=\left ( 5\hat{i}-\hat{j}-4\hat{k} \right )+\lambda \left ( 2\hat{i}-\hat{j}-\hat{k} \right )

Is parallel to the vector

\vec{b}= 2\hat{i}-\hat{j}+\hat{k}

Normal to the plane is

\vec{n}= 3\hat{i}-4\hat{j}-\hat{k}

Let \theta is the angle between line and plane

Then,

sin\theta =\frac{\left | \vec{b}.\vec{n} \right |}{\left | \vec{b} \right |\left | \vec{n} \right |}\Rightarrow \frac{\left | \left ( 2\hat{i}-\hat{j}+\hat{k} \right ).\left ( 3\hat{i}-4\hat{j}+\hat{k} \right ) \right |}{\sqrt{6}.\sqrt{26}}

=\frac{\left | 6+4-1 \right |}{\sqrt{156}}=\frac{9}{\sqrt{156}}

\theta = sin^{-1}\left [ \frac{9}{\sqrt{156}} \right ]

Posted by

Gurleen Kaur

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