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UPSC 2013 CDS 2 Math Paper
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© examsnet.com
Question : 10
Total: 100
If
x
+
y
–
7
=
0
and
3
x
+
y
–
13
=
0
, then what is
4
x
2
+
y
2
+
4
x
y
equal to?
[2013 CDS-II]
75
85
91
100
Validate
Solution:
The given equations are:
x
+
y
−
7
=
0
.......(1)
3
x
+
y
−
13
=
0
.....(2)
Subtracting (2) from (1), we get:
–
2
x
=
–
6
⇒
x
=
3
Putting
x
=
3
in (1), we get
y
=
4
∴
4
x
2
+
y
2
+
4
x
y
=
4
×
3
2
+
4
2
+
4
×
3
×
4
=
36
+
16
+
48
=
100
© examsnet.com
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