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The area of the region eclosed between the parabolas \mathrm{y^{2}=2x-1} and \mathrm{y^{2}=4x-3} is

 

Option: 1

\mathrm{\frac{1}{3}}


Option: 2

\mathrm{\frac{1}{6}}


Option: 3

\mathrm{\frac{2}{3}}


Option: 4

\mathrm{\frac{3}{4}}


Answers (1)

We have, \mathrm{y^{2}=2x-1}  ...........(1)

       and   \mathrm{y^{2}=4x-3}  .........(2)

We first find the point of inter section of the given parabolas by solving the eqn (1) and (2) simultaneously.

This gives, \mathrm{2x-1=4x-3}

          \Rightarrow \mathrm{2x=2\Rightarrow x=1}

Now, put \mathrm{x=1} in eqn (1), we get \mathrm{y=\pm 1}

Now the eqn(1) and (2) can be written as

        \mathrm{y^{2}=2\left ( x-\frac{1}{2} \right )}

        \mathrm{y^{2}=4\left ( x-\frac{3}{4} \right )} respectively.

The graphs of these two curves are

Now, the eqn (1) and (2) can be written as 

\mathrm{x=\frac{y^{2}+1}{2}}\: \&\: \mathrm{x=\frac{y^{2}+3}{4}}  respectively

 So   \mathrm{A=2\int _{0}^{1}\left ( x_{2}-x_{1} \right )dy}        

  ( \therefore Area is symmetrical about x-axis )

    Where  \mathrm{x_{1}=\frac{y^{2}+1}{2}\: and \: x_{2}=\frac{y^{2}+3}{4}}

       \mathrm{A=2\int _{0}^{1}\left ( \frac{y^{2}+3}{4}-\frac{y^{2}+1}{2} \right )dy\\

           =\mathrm{\frac{1}{2}\left[y-\frac{y^{3}}{3}\right]_{0}^{1}=\frac{1}{2}\left[1-\frac{1}{3} \right ]}\\

          =\mathrm{\frac{1}{2}\times \frac{2}{3}=\frac{1}{3}} sq.units

Hence he correct answer is option 1.

Posted by

Kshitij

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