Very strange shape

Calculus Level 3

There is a shape confined by the overlap of a circle and parabola. If the equation of this parabola is

x 2 = y x^2 = y

and the equation of the circle is

x 2 + y 2 = 1 x^2 + y^2 = 1

the area of this shape is α \alpha . Find α \lceil{\alpha}\rceil


The answer is 2.

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2 solutions

Julian Poon
Sep 13, 2014

This is a more exact answer.

We want to integrate y = x 2 y={ x }^{ 2 } and the limits would be the intersection to the 2 2 graphs. Then we would minus the resultant value from the area of the semicircle of the equation x 2 + y 2 = 1 { x }^{ 2 }+{ y }^{ 2 }=1 to get the answer.

Intersection of the two graphs: 1 x 2 = x 2 \sqrt { 1-{ x }^{ 2 } } ={ x }^{ 2 }

x = ± 1 2 [ 5 1 ] x=\pm\sqrt { \frac { 1 }{ 2 } \left[ \sqrt { 5 } -1 \right] }

So integrating: 1 2 [ 5 1 ] 1 2 [ 5 1 ] x 2 d x 0.32391 \int _{ -\sqrt { \frac { 1 }{ 2 } \left[ \sqrt { 5 } -1 \right] } }^{ \sqrt { \frac { 1 }{ 2 } \left[ \sqrt { 5 } -1 \right] } }{ { x }^{ 2 } } dx\approx 0.32391

And therefore, the answer is: 1 2 π 0.32391 = 1.25 = α ( 3 s . f ) \frac { 1 }{ 2 } \pi -0.32391=1.25=\alpha \quad (3s.f) α = 2 \left\lceil \alpha \right\rceil =\boxed{2}

Aditya Raut
Aug 24, 2014

First of all, a mistake in wording.I hope you mean area of the intersection, not parabola.

More of Logic than of maths, if time is a concern

The area of circle is π \pi sq. units img img

The shaded area is α \alpha . It's less than half area of circle and bigger than quarter area (note that B E C > 9 0 \angle BEC > 90^\circ )

Then we have π 4 < α < π 2 \displaystyle \dfrac{\pi}{4} < \alpha < \dfrac{\pi}{2}

Thus α = 1 \lceil \alpha \rceil = 1 or α = 2 \lceil \alpha \rceil = 2

Answer is eventually 2 \boxed{2} again, in at the most 2 2 attempts.

Changed the wording. Thanks. In your solution however, I do believe you mean π 4 < α < π 2 \frac {\pi}{4} < \alpha < \frac {\pi}{2}

Sharky Kesa - 6 years, 9 months ago

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LOLOLOL oops I also made a mistake in typing.

Aditya Raut - 6 years, 9 months ago

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