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Need solution for RD sharma maths class 12 chapter 28 The Plane exercise 28.8 question 13

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The answer of the given question is \vec{r}.\left ( 20\hat{i}+23\hat{j}+26\hat{k} \right )=69.

Hint:- We know that, equation of a plane passing through the line of intersection of two planes

a_{1}x+b_{1}y+c_{1}z+d_{1}=0 and a_{2}x+b_{2}y+c_{2}z+d_{2}=0  is given by
\left (a_{1}x+b_{1}y+c_{1}z+d_{1} \right )+k\left ( a_{2}x+b_{2}y+c_{2}z+d_{2} \right )=0

Given:-\vec{r}.(\hat{i}+\hat{j}+\hat{k})=6           and

\vec{r}.(2\hat{i}+3\hat{j}+4\hat{k})=-5  and Point (1,1,1)

Solution:-  The Cartesian equation of the given planes are x+y+z-6=0 and  2x+3y+4z+5=0

The family of planes is x+y+z-6+\lambda (2x+3y+4z+5)=0                      …(i)

Since it pass through (1,1,1)

1+1+1-6+\lambda(2+3+4+5)=0\\ -3+\lambda(14)=0\\ \lambda=\frac{3}{14}

x+y+z-6+\frac{3}{14} \left (2x+3y+4z+5 \right )=0\\ 14x+14y+14z-84+6x+9y+12z+15=0\\ 20x+23y+26z-69=0
Vector equation is  \vec{r}. (20\hat{i}+23\hat{j}+26\hat{k})=69

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