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Mathematics: Xy M M M 2, 3

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EBD_7801

2019 - 26

Mathematics (-3m + 15) m


Þ = -1 Þ m 2 - 5m + 6 = 0
-18
37. (b) xy £ 8, 1 £ y £ x2
Intersection points of xy = 8 and y = 1 is (8, 1); xy = 8 Þ m = 2, 3
and y = x2 is (2, 4) and y = x2 and y = 1 is (1, 1)
Y Alternately :- The x-coordinates of intersection
y = x2 points P and Q of circle and line can be given by
solving their equations for x.
(2, 4) Putting y = mx + 1 in (x –3)2 + (y + 2)2 = 25, we
xy get (x – 3) 2 + (mx + 3) 2 = 25
= 8 (8, 1) Þ (m2 + 1) x 2 + 6(m - 1) x - 16 = 0
(1, 1) y=1
-6( m - 1)
X' O X Þ x1 + x2 = where x1 and x2 are x-
m2 + 1
coordinates of P and Q respectively. As per
-3
question, x-coordinate of mid point of PQ is
Y' 5
2 8 8 x1 + x2 3 -3( m - 1) -3
2 8 \ =- Þ =
Required area = ò x dx + ò dx - ò1dx 2 5 m2 + 1 5
x
1 2 1
2 Þ m2 – 5m + 6 = 0 Þ m = 2, 3
æ x3 ö 39. (d) S : |z – 2 + i| ³ 5 represents boundary and outer
= ç ÷ + (8lnx)82 - (x)18
è 3 ø1 region of circle with centre (2, –1) and radius 5 .
8 1
= - + 8 ln 8 - 8ln 2 - (8 - 1) 1
3 3 z0 Î S, such that is the maximum.
7 14 | z0 - 1 |
= + 24 ln 2 - 8 ln 2 - 7 = 16 ln 2 -
3 3
\ |z0 –1| is minimum
\ correct option is (b)
z0 Î S with |z0 – 1| as minimum will be a point on
38. (a) Circle (x – 3)2 + (y + 2)2 = 25, with centre C(3, –2) and
boundary of circle of region S which lies on radius of
radius 5 is intersected by a line y = mx + 1 at p & Q
this circle, and passes through (1, 0).
such that mid point R of PQ has its
\ z0, 1, 2 – i are collinear, or (x0, y0), (1, 0),
3
x-coordinate as - . (2, –1) are collinear.
5
æ 3 -3m ö \ Using slopes of paralled lines,
Let R ç - , + 1÷
è 5 5 ø y0 -1
= Þ y0 = 1 – x0
x0 - 1 2 - 1
Y

y = mx + 1 P
R Q z0
O (1, 0)
X' X
O (2, –1)

C (3, –2)

4 - z0 - z0 4 - ( z0 + z0 )
Now, =
z0 - z 0 + 2i ( z0 - z0 ) + 2i
Y' 4 - 2 x0 4 - 2 x0 2(2 - x0 ) 1
-3m = = = = -i
+1 + 2 2iy0 + 2i 2i - 2 x0i + 2i
=
5 2(2 - x0 )i i
Then CR ^ PQ Þ ´ m = -1
3
- -3 æ 4 - z0 - z0 ö -p
5 \ Arg ç
z - z - 2i ÷ = Arg (–i ) = 2
è 0 0 ø

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