By Mansi Yadav

Verified by Ajay Kumar

If a, b, c are in A.P. and a^2, b^2, c^2 are in G.P., then what is the relation among a, b, c?

  1. a = b = c

  2. a + c = 2b and abc = 0

  3. b² = ac

  4. a² + c² = 2b²

Answer: D

Solution

Solution: Since a, b, c are in A.P., \(a+c=2b\). Since a², b², c² are in G.P., \((b^2)^2=a^2c^2\), giving \(b^2=ac\) under the usual positive-term assumption. Squaring \(a+c=2b\), \(a^2+2ac+c^2=4b^2\). Substituting \(ac=b^2\), we get \(a^2+c^2=2b^2\). Trick: Combine the A.P. condition with the G.P. condition, then square the A.P. relation.

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