Q20 / 54 · JEE Advanced 2016 (Paper 2) · Mathematics

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

  • A
    16
  • B
    43
  • Correct answer
    C
    32
  • D
    53

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.
Figure
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

Hence, the correct answer is option: 'C'.

Relevant Questions