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The area (in sq. units) of the bigger portion of region enclosed by the curves 4x2+9y2=364x^2 + 9y^2 = 36 and 2x+3y=62x + 3y = 6 is

Solution

Correct Option: 2

The given curves are:

4x2+9y2=36    x29+y24=14x^2 + 9y^2 = 36 \implies \dfrac{x^2}{9} + \dfrac{y^2}{4} = 1

So a=3a = 3 and b=2b = 2.

2x+3y=6    x3+y2=12x + 3y = 6 \implies \dfrac{x}{3} + \dfrac{y}{2} = 1

The intercept form tells us the line passes through (3,0)(3, 0) and (0,2)(0, 2). Both points satisfy the ellipse equation, so the line meets the ellipse at exactly these two points and cuts it into two parts.


Total area of the ellipse:

Aellipse=πab=π(3)(2)=6πA_{\text{ellipse}} = \pi a b = \pi(3)(2) = 6\pi


The smaller portion lies in the first quadrant between the ellipse (above) and the line (below).

Asmall=03[239x262x3]dxA_{\text{small}} = \displaystyle\int_0^3 \left[\frac{2}{3}\sqrt{9 - x^2} - \frac{6 - 2x}{3}\right] dx


Evaluating the ellipse part:

03239x2dx=23039x2dx\displaystyle\int_0^3 \frac{2}{3}\sqrt{9 - x^2}\, dx = \frac{2}{3} \int_0^3 \sqrt{9 - x^2}\, dx

Using 0aa2x2dx=πa24\displaystyle\int_0^a \sqrt{a^2 - x^2}\, dx = \frac{\pi a^2}{4}:

=23×9π4= \dfrac{2}{3} \times \dfrac{9\pi}{4}

=3π2= \dfrac{3\pi}{2}


Evaluating the line part:

0362x3dx=13[6xx2]03\displaystyle\int_0^3 \frac{6 - 2x}{3}\, dx = \frac{1}{3}\Big[6x - x^2\Big]_0^3

=13(189)= \dfrac{1}{3}(18 - 9)

=3= 3


Asmall=3π23A_{\text{small}} = \dfrac{3\pi}{2} - 3


Abig=AellipseAsmallA_{\text{big}} = A_{\text{ellipse}} - A_{\text{small}}

=6π(3π23)= 6\pi - \left(\dfrac{3\pi}{2} - 3\right)

=6π3π2+3= 6\pi - \dfrac{3\pi}{2} + 3

=12π3π2+3= \dfrac{12\pi - 3\pi}{2} + 3

=9π2+3= \dfrac{9\pi}{2} + 3

=9π+62= \dfrac{9\pi + 6}{2}

=32(3π+2)= \dfrac{3}{2}(3\pi + 2)

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