Mathematics - Area Under Curves Question with Solution | TestHub

MathematicsArea Under CurvesArea bounded by two curvesMedium2 minPYQ_2016
MathematicsMediumsingle choice

Area of the region{x,y∈R2: y≥x+3,5y≤x+9≤15}is equal to

Options:

Answer:
C
Solution:

If x+3<0⇒y≥ −(x+3)    & y≥0
If x+3≥0⇒y≥ (x+3)       & y≥0
Also
5y≤x+9≤15
⇒x−5y+9≥0   &   x≤6
Intersection point of line & parabolas
5y=x+9    &     y 2 =| x+3 | (y≥0)
( x+9 5 ) 2 =| x+3 |
x 2 +18x+81=25x+75  or  −25x−75
x 2 −7x+6=0  or   x 2 +43x+156=0
x=1,6       or     x=−39,−4
So Clearly,   x=1,y=2
and when  x=−4,y=1 are required points
Drawing all these, we get this graph.

Shaded portion is required area.
Clearly required area = area (trapezium ABCD) - A1+A2 .......(i)
area (trapezium ABCD) =121+25=152
A1= ∫-4-3-x+3dx
=23
and A1= ∫-31x+312dx=163
∴ From equation (i), we get required area =152-23+163=32

Stream:JEE_ADVSubject:MathematicsTopic:Area Under CurvesSubtopic:Area bounded by two curves
⏱ 2mℹ️ Source: PYQ_2016

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