Sketch the region common to the circlex2+y2=25and the parabola y2=8x. Also, find the area of the region, using integration.
Given the boundaries of the area to be found are,
• the circle, x2 + y2 = 25 ---(1)
• the parabola, y2 = 8x ---- (2)
From the equation, of the first circle, x2 + y2 = 25
• the vertex at (0,0) i.e. the origin
• the radius is 5 units.
From the equation, of the parabola , y2 = 8x
• the vertex at (0,0) i.e. the origin
• Symmetric about the x-axis, as it has the even power of y.
Now to find the point of intersection of (1) and (2), substitute y2 = 8x in (1)
x2 + 8x = 25
x2 + 8x - 25= 0
as y cannot be imaginary, we reject the negative value of x
so
So the two points, A and B are the points where (1) and (2) meet.
The line AB meets the x-axis at D = [(√41 -4),0]
Substitute y = 0 in (1),
x2 + 0 = 25
x = ±5
So the circle intersects the x-axis at C(5,0)and E(-5,0)
As x and y have even powers for the circle, they will be symmetrical about the x-axis and y-axis.
Consider the circle, x2 + y2 = 25, can be re-written as
----- (3)
Consider the parabola, y2 = 8x, can be re-written as
----- (4)
Now, the area to be found will be the area is
Area of the required region = Area of OACBO.
Area of OABCO= Area of OCAO+ Area of OCBO
[area of OCBO= area of OCAOas the circle is symmetrical about the y-axis]
Area of OACBO= 2 × Area of OCAO---- (5)
Area of OCAO= Area of OADO+ Area of DACD
Area of OCAOis
[Using the formula, and ]
Let √41 – 4 = a
[sin-1(1) = 90° and sin-1(0) = 0°]
The Area of OCAOsq. units, where a = √41 - 4
Now substituting the area of OCAOin equation (5)
Area of OACBO= 2 × Area of OCAO
Area of the required region is sq. units, where a = √41 - 4