JAMIA 2021 — Mathematics PYQ
JAMIA | Mathematics | 2021If slope of common tangent to curves 4x2+9y2=36 and 4x2+ 4y2= 31 is m, then m2 is equal to:
Choose the correct answer:
- A.
3
(Correct Answer) - B.
6
- C.
9
- D.
5
3
Explanation
Curve 1: Ellipse
364x2+369y2=1⟹9x2+4y2=1
Here, a2=9 and b2=4.
The equation of a tangent with slope m is:
y=mx±a2m2+b2
y=mx±9m2+4…(1)
Curve 2: Circle
4x2+4y2=31⟹x2+y2=431
The radius squared is r2=431.
The equation of a tangent with slope m is:
y=mx±r1+m2
y=mx±431(1+m2)…(2)
Condition for Common Tangent
Equating the constant terms from (1) and (2):
9m2+4=431(1+m2)
4(9m2+4)=31(1+m2)
36m2+16=31+31m2
36m2−31m2=31−16
5m2=15
m2=3
Final Answer:
m2=3
Explanation
Curve 1: Ellipse
364x2+369y2=1⟹9x2+4y2=1
Here, a2=9 and b2=4.
The equation of a tangent with slope m is:
y=mx±a2m2+b2
y=mx±9m2+4…(1)
Curve 2: Circle
4x2+4y2=31⟹x2+y2=431
The radius squared is r2=431.
The equation of a tangent with slope m is:
y=mx±r1+m2
y=mx±431(1+m2)…(2)
Condition for Common Tangent
Equating the constant terms from (1) and (2):
9m2+4=431(1+m2)
4(9m2+4)=31(1+m2)
36m2+16=31+31m2
36m2−31m2=31−16
5m2=15
m2=3
Final Answer:
m2=3

