Mathematics_Today_-_October_2016

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  1. (8) : 2 ≥ max.{|x – y|, |x + y|}
    ⇒ |x – y| ≤ 2 and |x + y| ≤ 2, which forms a square
    of diagonal length 4 units.
    
    2


–2

 2 



–=–2

+= 2 –= 2

+=–2


⇒ The area of the region =


1
2

××= 448 sq. units.


  1. (4) : Area = 4
    0


1
∫|ln |xdx

=−^4 ∫
0


1
lnxdx=− 4 []xxxln − 01 = 4 sq. units


  1. (7) : Then required area will be equal to area
    enclosed by y = f (x), the y-axis between the abscissa
    at y = –2 and y = 6.
    = 6


(0, 2)
–1  

=–2







Required area = { 62 ( )} [ ( ) ( )]
0


1

1

0
∫∫− + −−

fx dx fx dx

⇒ 9
2


=m ⇒− 27 =
n

m


  1. (0) : I= ∫ 2 t tdt
    4


2
sin cos
/

/

π

π


  • ∫{( sin cos ) (sin cos )}− ++∫ − sin cos


/

/

tt ttdt 2 ttdt

54

2 π

π

π

π

= ∫∫sin − sin =
/

//
220
4

254
tdt tdt
π

π

π

π


  1. (6) :
    Area=∫()()6543−− − −−^22 ∫
    1


3

1

5
xx dx xx dx

+∫() 43 −−^2 +∫() 315 −
3

4

4

5
xx dx xdx

=^73
6

sq. units


  1. (8) : ′ =


+ − +

fx fx h fx
h h

( ) lim ()()
0

0

= ++ −−−

lim () () () () () ()
h

fx fh h fx fx f fx
0 h

00

= −


⎝⎜


lim→ ⎠⎟+
() () ()
h

fh f
h

fx
0

0
0

⇒ fx′()= fx() ⇒

′ =
∫∫

fx
fx

()dx dx
()

⇒ (^2) fx x c()=+ ⇒ fx()=x
2
4
When α = 0, area is minimum.
Required minimum area = 22
0
9
∫ ydy
= ⎛
⎝⎜

⎠⎟
4 =
32
72
32
0
9
y/
/
sq. units.



  1. (8) : x^2 + y^2 ≤ 144 and sin(x + y) ≥ 0
    ⇒ 2 nπ ≤ x + y ≤ (2n + 1)π ; n ∈I
    Hence, we get the area


S=π⋅ ⇒ S=
π

144
29

8


  1. (1) : Area = n + 1


+ 1

–1



1
+ 1



””
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