NIMCET 2014 — Mathematics PYQ
NIMCET | Mathematics | 2014If the foci of the ellipse b2x2+16y2=16b2 and the hyperbola 81x2−144y2=2581×144 coincide, then the value of b, is:
Choose the correct answer:
- A.
1
- B.
5
- C.
7
(Correct Answer) - D.
3
7
Explanation
Calculation for Hyperbola:
81x2−144y2=2581×144
⇒14425x2−8125y2=1
∴ah2=25144 and bh2=2581
eh2=1+(ah2bh2)
⇒eh2=1+(14481)
⇒eh2=144225⇒eh=1215
Fh=(aheh,0)=(512×1215,0)
⇒Fh=(3,0)
Calculation for Ellipse:
b2x2+16y2=16b2
⇒16x2+b2y2=1
∴ae2=16 and be2=b2
Fe=(aeee,0)=(4ee,0)
Given: Fe=Fh
⇒(4ee,0)=(3,0)
⇒4ee=3⇒ee=43
ee2=1−(ae2be2)
⇒(43)2=1−(42b2)
⇒1−169=16b2
⇒b2=7⇒b=7
Explanation
Calculation for Hyperbola:
81x2−144y2=2581×144
⇒14425x2−8125y2=1
∴ah2=25144 and bh2=2581
eh2=1+(ah2bh2)
⇒eh2=1+(14481)
⇒eh2=144225⇒eh=1215
Fh=(aheh,0)=(512×1215,0)
⇒Fh=(3,0)
Calculation for Ellipse:
b2x2+16y2=16b2
⇒16x2+b2y2=1
∴ae2=16 and be2=b2
Fe=(aeee,0)=(4ee,0)
Given: Fe=Fh
⇒(4ee,0)=(3,0)
⇒4ee=3⇒ee=43
ee2=1−(ae2be2)
⇒(43)2=1−(42b2)
⇒1−169=16b2
⇒b2=7⇒b=7