Practicing Success

Target Exam

CUET

Subject

-- Mathematics - Section A

Chapter

Application of Integrals

Question:

The area inside the parabola 5x2 - y = 0 but outside the parabola 2x2 - y + 9 = 0 is:

Options:

$9\sqrt{3}$

$8\sqrt{3}$

$12\sqrt{3}$

$2\sqrt{3}$

Correct Answer:

$12\sqrt{3}$

Explanation:

Eliminating y, we get : 54x2 - (2x2 + 9) = 0 or 3x2 = 9 $x = -\sqrt{3}, 3$

The two parabolas are $x^2=\frac{1}{2}y,\,x^2=\frac{1}{2}(y-9)$ and clearly from the figure second parabola is upper and first is lower.

∴ Required area = $2\int_0^{\sqrt{3}}(y_1-y_2)dx$ ... (i)

$=2\int\limits_0^{\sqrt{3}}[(2x^2+9)-5x^2].dx=2\int\limits_0^{\sqrt{3}}(9-3x^2).dx=12\sqrt{3}$