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Please solve RD Sharma class 12 chapter The Plane exercise 28.8 question 17 maths textbook solution

Answers (1)

Answer:-  The answer of the given question is x+y+z=a+b+c.

Hints:-  By substituting \vec{r}=x \hat{\imath}+y \hat{j}+z \hat{k} in equation (ii)

Given:-  (a, b, c) and parallel to plane \vec{r} \cdot(\hat{\imath}+\hat{\jmath}+\hat{k})=2                 

Solution:-  Any plane passes through the point (a, b, c) and parallel to plane \vec{r} \cdot(\hat{\imath}+\hat{\jmath}+\hat{k})=2 is given by

        \vec{r} \cdot(\hat{\imath}+\hat{\jmath}+\hat{k})=\lambda…(i)

Here, the position vector \vec{r} of this point is \vec{r}=a \hat{\imath}+b \hat{\jmath}+c \hat{k}

∴ Equation (i) becomes        

        \begin{gathered} (a \hat{\imath}+b \hat{\jmath}+c \hat{k}) \cdot(\hat{\imath}+\hat{\jmath}+\hat{k})=\lambda \\\\ \Rightarrow a+b+c=\lambda \end{gathered}

Substituting \lambda =a+b+c in equation (i), we obtain

        \vec{r} \cdot(\hat{\imath}+\hat{\jmath}+\hat{k})=a+b+c         … (ii)

This is vector equation of the required plane

Substituting \vec{r}=x \hat{\imath}+y \hat{\jmath}+z \hat{k} in equation (ii)


        \begin{gathered} (x \hat{\imath}+y \hat{\jmath}+z \hat{k}) \cdot(\hat{\imath}+\hat{\jmath}+\hat{k})=a+b+c \\\\ x+y+z=a+b+c \end{gathered}

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