Calculate the area

Calculus Level 4

If the area between the curves { x 2 + y 2 = 3 x + y = 3 \begin{cases} \quad x^2+y^2=3 \\ \sqrt{|x|}+\sqrt{|y|}=\sqrt{\sqrt{3}} \end{cases} is ( λ × π ϕ ) s q . u n i t s (\lambda \times \pi - \phi) \ sq. \ units ,

then find the value of λ × ϕ \lambda \times \phi

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The answer is 6.

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3 solutions

Pranjal Jain
Dec 13, 2014

We are going to use symmetry, and definite integration (using walli's) to get the answer

Area between curves = 4 × =4× Area between curves in first quadtant

Parametric form of curve is ( 3 cos 4 θ , 3 sin 4 θ ) (\sqrt{3}\cos^{4}\theta,\sqrt{3}\sin^{4}\theta)

d y = 4 3 sin 3 θ cos θ d θ dy=4\sqrt{3}\sin^{3}\theta \cos\theta d\theta

= 4 × =4× (Area under circle-Area under curve)

= 4 × ( 3 π 4 0 π 212 cos 5 θ sin 3 θ d θ =4×(\frac{3\pi}{4}-\displaystyle\int_{0}^{\pi}{2} 12\cos^{5}\theta \sin^{3}\theta d\theta

= 3 π 48 × ( 4 × 2 ) ( 2 ) 8 × 6 × 4 × 2 =3\pi-48×\frac{(4×2)(2)}{8×6×4×2} (Using walli’s formula) \color{#3D99F6}{\text{(Using walli's formula)}}

= 3 π 2 =3\pi-2

λ = 3 , ϕ = 2 \lambda=3,\phi=2

λ × ϕ = 6 \lambda×\phi=\boxed{6}

Pranjal, Do you study at FIITJEE?

A Former Brilliant Member - 6 years, 5 months ago
Nishant Sharma
Nov 26, 2014

This is the graph of the given system of equations:

graph graph where the blue colour represents the circle x 2 + y = 3 x^2+y^=3 and the red colour represents the curve x + y = 3 1 / 4 \displaystyle\,\sqrt{|x|}+\sqrt{|y|}=3^{1/4} .

Now the shaded region is the required area which is given by 4 × ( 0 3 3 y 2 ( 3 1 / 4 y ) 2 d x ) = 3 π 2 4\times\left(\displaystyle\int_{0}^{\sqrt{3}} \sqrt{3-y^2}-(3^{1/4}-\sqrt{|y|})^2\, \mathrm{d}x\,\right)=\,\displaystyle\boxed{3\pi-2} . So required value is 3 × 2 = 6 3\times2=\boxed{6} .

NOTE: A better phrasing would be ( λ × π + ϕ ) \left(\lambda\times\pi+\phi\right) to avoid ambiguity which would yield the answer -6 since it is unstated whether ϕ > 0 \phi>0 or ϕ < 0 \phi<0 .

Circl equation is x^2 + y^2 = 3 not x^2 + y = 3. Please correct it.

Vijay Simha - 1 year, 11 months ago
Prakhar Bindal
Oct 6, 2016

i think all solution involve a bit complex integrals.

The Area required = area of circle -4*area of curve in first quadrant

The latter is readily evaluated by taking curve in first quadrant

And using integral of ydx!

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