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Need solution for RD Sharma Maths Class 12 Chapter 28 The Plane Excercise 28.11 Question 25

Answers (1)

Answer:  x+2 y+3 z-3=0

Hint: Use formula  \frac{x-x_{1}}{a_{1}}=\frac{y-y_{1}}{b_{1}}=\frac{z-z_{1}}{c_{1}}

Given: Points  (-1,2,0) \&(2,2,-1)   and line  \frac{x-1}{1}=\frac{2 y+1}{2}=\frac{z+1}{-1}

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 ( -1,2,0 \right )  is

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

It also passes through \left ( 2,2,-1 \right )

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

            \begin{aligned} &a(2+1)+b(2-2)+c(-1-0)=0 \\ & \end{aligned}

            \Rightarrow 3 a-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  a_{1} a_{2}+b_{1} b_{2}+c_{1} c_{2}=0                                              ………… (4)

Here the plane is parallel to line

            \frac{x-1}{1}=\frac{2 y+1}{2}=\frac{z+1}{-1}

So, a \times 1+b \times 1+c \times-1=0 \\

            \Rightarrow a+b-c=0                                                               ………… (5)

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

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

            \Rightarrow \frac{a}{1}=\frac{b}{2}=\frac{c}{3}=k(\text { say })

            a=k, b=2 k, c=3 k

Putting the value in equation (2) we get

             \begin{aligned} &k(x+1)+2 k(y-2)+3 k(z-0)=0 \\ & \end{aligned}

             k x+k+2 k y-4 k+3 k z=0

Dividing by k we have,

            x+2 y+3 z-3=0

The required equation is  x+2 y+3 z-3=0

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