Q111 / 180 · COMEDK 2026 (9 May Shift 2) · Mathematics
The area enclosed by the curve $y = -x^2$ and the line $x + y + 2 = 0$ is
- Correct answerA$4.5$ sq units
- B$3.5$ sq units
- C$5.5$ sq units
- D$4$ sq units
Solution
Find the points of intersection of the curve $y = -x^2$ and the line $x + y + 2 = 0$.
Substituting $y = -x^2$ into the line equation:
$x - x^2 + 2 = 0$
$x^2 - x - 2 = 0$
$(x - 2)(x + 1) = 0$
The points of intersection are at $x = -1$ and $x = 2$.
In the interval $[-1, 2]$, the parabola $y = -x^2$ lies above the line $y = -x - 2$.
The required area is given by:
$A = \int_{-1}^{2} [(-x^2) - (-x - 2)] dx$
$A = \int_{-1}^{2} (-x^2 + x + 2) dx$
$A = \left[ -\dfrac{x^3}{3} + \dfrac{x^2}{2} + 2x \right]_{-1}^{2}$
$A = \left( -\dfrac{8}{3} + \dfrac{4}{2} + 4 \right) - \left( \dfrac{1}{3} + \dfrac{1}{2} - 2 \right)$
$A = \left( 6 - \dfrac{8}{3} \right) - \left( \dfrac{5}{6} - 2 \right)$
$A = \dfrac{10}{3} - \left( -\dfrac{7}{6} \right)$
$A = \dfrac{20}{6} + \dfrac{7}{6} = \dfrac{27}{6} = 4.5$ sq units.
Answer: $4.5$ sq units
Substituting $y = -x^2$ into the line equation:
$x - x^2 + 2 = 0$
$x^2 - x - 2 = 0$
$(x - 2)(x + 1) = 0$
The points of intersection are at $x = -1$ and $x = 2$.
In the interval $[-1, 2]$, the parabola $y = -x^2$ lies above the line $y = -x - 2$.
The required area is given by:
$A = \int_{-1}^{2} [(-x^2) - (-x - 2)] dx$
$A = \int_{-1}^{2} (-x^2 + x + 2) dx$
$A = \left[ -\dfrac{x^3}{3} + \dfrac{x^2}{2} + 2x \right]_{-1}^{2}$
$A = \left( -\dfrac{8}{3} + \dfrac{4}{2} + 4 \right) - \left( \dfrac{1}{3} + \dfrac{1}{2} - 2 \right)$
$A = \left( 6 - \dfrac{8}{3} \right) - \left( \dfrac{5}{6} - 2 \right)$
$A = \dfrac{10}{3} - \left( -\dfrac{7}{6} \right)$
$A = \dfrac{20}{6} + \dfrac{7}{6} = \dfrac{27}{6} = 4.5$ sq units.
Answer: $4.5$ sq units
Hence, the correct answer is option: 'A'.