The area (in sq. units) of the region $\{(x,y): 3x^2≤ y ≤ |x|\}$ is equal to
Answer & explanation
Correct answer: option 3
The correct answer is Option (3) → $\frac{1}{27}$
Region is defined by
$3x^2\le y\le |x|$
Points of intersection are obtained from
$3x^2=|x|$
$|x|=3x^2$
For $x\ge0$
$x=3x^2$
$3x^2-x=0$
$x(3x-1)=0$
$x=0,\;\frac{1}{3}$
For $x\le0$
$-x=3x^2$
$3x^2+x=0$
$x(3x+1)=0$
$x=0,\;-\frac{1}{3}$
Area is symmetric about $y$-axis
$\text{Area}=2\int_{0}^{1/3}\left(|x|-3x^2\right)dx$
For $x\ge0,\;|x|=x$
$=2\int_{0}^{1/3}(x-3x^2)\,dx$
$=2\left[\frac{x^2}{2}-x^3\right]_{0}^{1/3}$
$=2\left(\frac{1}{18}-\frac{1}{27}\right)$
$=2\cdot\frac{1}{54}$
$=\frac{1}{27}$
The required area is $\frac{1}{27}$ square units.