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Explain solution RD Sharma class 12 chapter 28 The Plane exercise very short answer type question 16 maths

Answers (1)

Answer:

 -\frac{13}{4}

Hint:

 Use this formula if two planes are perpendicular a1a2+b1b2+c1c2=0

Given:

 \frac{x-1}{2}=\frac{y-1}{3}=\frac{z-1}{k} \perp \text { to normal of plane } \overrightarrow{r}.(2\widehat{i}+3\widehat{j}+4\widehat{k})=4

Solution:

\overrightarrow{r}.(2\widehat{i}+3\widehat{j}+4\widehat{k})=4 \qquad \qquad \dots(i)

So the vector normal to the plane as,

\overrightarrow{n}=2\widehat{i}+3\widehat{j}+4\widehat{k}

a1 = 2, b1 = 3, c1 = 4

and

\frac{x-1}{2}=\frac{y-1}{3}=\frac{z-1}{k} \qquad \qquad \dots (ii)

a2 = 2, b2 = 3, c2 = k

Since (i) and (ii) ⊥ to each other.

\begin{aligned} &a_1a_2+b_1b_2+c_1C_2=0\\ &2.2+3.3+4.k=0\\ &\Rightarrow 4+9+4k=0\\ &\Rightarrow 4k=-13\\ &\Rightarrow k=-\frac{13}{4} \end{aligned}

Posted by

Gurleen Kaur

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