Find the area bounded by the parabola y2 = 4x and the line y = 2x – 4.
(i) By using horizontal strips
(ii) By using vertical strips.
Given: - Two curves are y2 = 4x and y = 2x – 4
Now to find the area between these two curves, we have to find common area i.e. Shaded portion
Intersection of parabola y2 = 4x with line y = 2x – 4
Putting the value of y from the equation of a line in parabola equation, we get,
y2 = 4x
⇒ (2x – 4)2 = 4x
⇒ 4x2 – 16x + 16 = 4x
⇒ 4x2 – 20x + 16 = 0
⇒ 4x2 – 16x – 4x + 16 = 0
⇒ 4x(x – 4) – 4(x – 4) = 0
⇒ 4(x – 1)(x – 4) = 0
⇒ (x – 1)(x – 4) = 0
⇒ x = 1,4
When x = 1, y = √4x
⇒ y = + 2, – 2; we take – 2 as the intersection is in the 4th quadrant and when x = 4, y = √4x
⇒ y = + 4, – 4; we take + 4 as the intersection is in 1st quadrant
Therefore intersection points are B(4,4) and C(1, – 2)
Area of the bounded region, taking strips
i) By using horizontal strips
Therefore, limits are for y and integrating with respect to y
Area bounded by region = {Area under line from – 2 to 4} –{Area under parabola from – 2 to 4}
Putting limits, we get
ii) By using vertical strips.
Therefore, limits are for x, and integrating with respect to x
Area bounded by region = {2(Area under parabola from 0 to 1) + (Area under parabola from 1 to 4)} – {Area under line from 1 to 4}
Tip: - Parabola is symmetrical about x - axis therefore its area is twice the area above x - axis. So, till its latus rectum i.e here a = 1, area is twice the area above x - axis.
Putting limits, we get,
Hence from both methods we get same answer