NIMCET 2015 — Mathematics PYQ
NIMCET | Mathematics | 2015If a,b and c are in geometric progression, then logaxx,logbxx and logcxx are in:
Choose the correct answer:
- A.
arithmetic progression
- B.
geometric progression
- C.
harmonic progression
(Correct Answer) - D.
arithmetico-geometric progression
harmonic progression
Explanation
Given a,b,c are in G.P., therefore:
Taking log with base x on both sides:
This shows that logxa,logxb,logxc are in A.P.
Now, add 2logxx (which is 2) to the equation:
This implies logx(ax),logx(bx),logx(cx) are in A.P.
We know that lognm=logmn1. Therefore:
By definition, if the reciprocals of a sequence are in A.P., the sequence itself is in Harmonic Progression (H.P.).
Correct Option: (c)
Explanation
Given a,b,c are in G.P., therefore:
Taking log with base x on both sides:
This shows that logxa,logxb,logxc are in A.P.
Now, add 2logxx (which is 2) to the equation:
This implies logx(ax),logx(bx),logx(cx) are in A.P.
We know that lognm=logmn1. Therefore:
By definition, if the reciprocals of a sequence are in A.P., the sequence itself is in Harmonic Progression (H.P.).
Correct Option: (c)