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Need solution for RD Sharma maths class 12 chapter 28 The Plane exercise very short answer type question 23

Answers (1)

Answer:

 x + y + z = 15

Hint:

 we will use equation of plane as lx + my + nz = d

Given:

 Distance from the origin 5\sqrt{3}

Solution:

Since the normal of plane equation inclined to co-ordinate axes

\therefore cos \: \alpha =cos\: \beta =cos\: \gamma

We know that

\begin{aligned} &cos^2 \: \alpha +cos^2\: \beta +cos^2\: \gamma =1\\ &\Rightarrow 3cos^2\alpha =1\\ &\Rightarrow cos\: \alpha =\frac{1}{\sqrt{3}}\\ &cos \: \alpha =cos\: \beta =cos\: \gamma =\frac{1}{\sqrt{3}}\\ &l=\frac{1}{\sqrt{3}},\; m=\frac{1}{\sqrt{3}},\;n= \frac{1}{\sqrt{3}} \end{aligned}

∴Equation of plane  lx + my + nz = d, d = distance from origin \begin{aligned} &(5\sqrt{3}) \end{aligned}

\begin{aligned} &\Rightarrow \frac{1}{\sqrt{3}}x+\frac{1}{\sqrt{3}}y+\frac{1}{\sqrt{3}}z=5\sqrt{3}\\ &\Rightarrow x + y+z =15 \end{aligned}

Posted by

Gurleen Kaur

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