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Please solve RD Sharma class 12 chapter The Plane exercise 28.8 question 13 maths textbook solution

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Answer:-  The answer of the given question is \vec{r} \cdot(20 \hat{\imath}+23 \hat{\jmath}+26 \hat{k})=69

Hints:- 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 \text { 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} \cdot(\hat{\imath}+\hat{\jmath}+\hat{k})=6        and

            \vec{r} \cdot\left(2 \hat{\imath}+\widehat{3}_{j}+4 \hat{k}\right)=-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 isx+y+z-6+\lambda(2 x+3 y+4 z+5)=0       …(i)

Since it pass through (1,1,1)
                \begin{gathered} 1+1+1-6+\lambda(2+3+4+5)=0 \\\\ -3+\lambda(14)=0 \\ \lambda=\frac{3}{14} \end{gathered}
            \begin{gathered} x+y+z-6+\frac{3}{14}(2 x+3 y+4 z+5)=0 \\\\ 14 x+14 y+14 z-84+6 x+9 y+12 z+15=0 \\\\ 20 x+23 y+26 z-69=0 \end{gathered}

Vector equation is  \vec{r} \cdot(20 \hat{\imath}+23 \hat{\jmath}+26 \hat{k})=69

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