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Need solution for RD Sharma Maths Class 12 Chapter 28 The Plane Excercise 28.11 Question 19

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Answer: Therefore, required equation of plane is  8 x-13 y+15 z+13=0

Hint: Use formula  a\left(x-x_{1}\right)+b\left(y-y_{1}\right)+c\left(z-z_{1}\right)=0

Given:  \frac{x+3}{2}=\frac{y-3}{7}=\frac{z-2}{5}

Solution: We know that the equation of plane passing through \left(\mathrm{x}_{1}, \mathrm{y}_{1}, \mathrm{z}_{1}\right)  is given by

            a\left(x-x_{1}\right)+b\left(y-y_{1}\right)+c\left(z-z_{1}\right)=0                             ……………… (1)

So, equation of plane passing through  \left ( 3,4,1 \right ) is

            a(x-3)+b(y-4)+c(z-1)=0                                 ……………… (2)

It also passes through \left ( 0,1,0 \right )

So, equation (2) must satisfy the point  \left ( 0,1,0 \right )

            \begin{aligned} &a(0-3)+b(1-4)+c(0-1)=0 \\ \end{aligned}

            \Rightarrow-3 a-3 b-c=0 \\

            \Rightarrow 3 a+3 b+c=0                                                        ……………… (3)

We know that line \frac{x-x_{1}}{a_{1}}=\frac{y-y_{1}}{b_{1}}=\frac{z-z_{1}}{c_{1}}  is parallel to plane a_{2} x+b_{2} y+c_{2} z+d_{2}=0  if

            \begin{aligned} &a_{1} a_{2}+b_{1} b_{2}+c_{1} c_{2}=0 \\ & \end{aligned}                                                   ……………… (4)

So,       a \times 2+b \times 7+c \times 5=0 \\

            \Rightarrow 2 a+7 b+5 c=0                                                      ………………. (5)

Solving equation (3) and (5) by cross a multiplication, we have

            \begin{aligned} &\frac{\mathrm{a}}{3 \times 5-(7) \times 1}=\frac{\mathrm{b}}{2 \times 1-3 \times 5}=\frac{\mathrm{c}}{3 \times 7-2 \times 3} \\ & \end{aligned}

            \Rightarrow \frac{\mathrm{a}}{15-7}=\frac{\mathrm{b}}{2-15}=\frac{\mathrm{c}}{21-6}

            \begin{aligned} &\Rightarrow \frac{a}{8}=\frac{b}{-13}=\frac{c}{15}=k(s a y) \\ \end{aligned}

                 a=8 k, b=-13 k, c=15 k

Putting the value in equation (2) we get

            \begin{aligned} &8 k(x-3)-13 k(y-4)+15 k(z-1)=0 \\ & \end{aligned}

            8 k x-24 k-13 k y+52 k+15 k z-15 k=0

Dividing by k we have

            8 x-13 y+15 z+13=0

Equation of required plane is  8 x-13 y+15 z+13=0

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