Q178 / 240 · KCET 2026 · Mathematics
The area of the region bounded by the curve $y^2 = x^3$, the $y$-axis and the lines $y = 1$ and $y = 8$ is
- A$\dfrac{155}{3}$ sq. units
- Correct answerB$\dfrac{93}{5}$ sq. units
- C$93$ sq. units
- D$155$ sq. units
Solution
The equation of the curve is given by $y^2 = x^3$, which can be written as $x = y^{2/3}$.
The required area is bounded by the curve $x = y^{2/3}$, the $y$-axis ($x = 0$), and the horizontal lines $y = 1$ and $y = 8$.
The area $A$ is given by the definite integral with respect to $y$:
$A = \int_{1}^{8} x \, dy$
Substituting $x = y^{2/3}$:
$A = \int_{1}^{8} y^{2/3} \, dy$
Integrating the function:
$A = \left[ \dfrac{y^{5/3}}{5/3} \right]_{1}^{8}$
$A = \dfrac{3}{5} \left[ y^{5/3} \right]_{1}^{8}$
Evaluating the limits:
$A = \dfrac{3}{5} \left( 8^{5/3} - 1^{5/3} \right)$
Since $8^{5/3} = (2^3)^{5/3} = 2^5 = 32$ and $1^{5/3} = 1$:
$A = \dfrac{3}{5} (32 - 1)$
$A = \dfrac{3}{5} \times 31 = \dfrac{93}{5}$ sq. units.
Answer: $\dfrac{93}{5}$ sq. units
The required area is bounded by the curve $x = y^{2/3}$, the $y$-axis ($x = 0$), and the horizontal lines $y = 1$ and $y = 8$.
The area $A$ is given by the definite integral with respect to $y$:
$A = \int_{1}^{8} x \, dy$
Substituting $x = y^{2/3}$:
$A = \int_{1}^{8} y^{2/3} \, dy$
Integrating the function:
$A = \left[ \dfrac{y^{5/3}}{5/3} \right]_{1}^{8}$
$A = \dfrac{3}{5} \left[ y^{5/3} \right]_{1}^{8}$
Evaluating the limits:
$A = \dfrac{3}{5} \left( 8^{5/3} - 1^{5/3} \right)$
Since $8^{5/3} = (2^3)^{5/3} = 2^5 = 32$ and $1^{5/3} = 1$:
$A = \dfrac{3}{5} (32 - 1)$
$A = \dfrac{3}{5} \times 31 = \dfrac{93}{5}$ sq. units.
Answer: $\dfrac{93}{5}$ sq. units
Hence, the correct answer is option: 'B'.