For any three positive real numbers a ,   b and c . If 9 25 a 2 + b 2 + 25 c 2 - 3 a c = 15 b 3 a + c .…

For any three positive real numbers a, b and c. If 925a2+b2+25c2-3ac=15b3a+c. Then
  1. b, c and a are in G.P.
  2. b, c and a are in A.P.
  3. a, b and c are in A.P.
  4. a, b and c are in G.P.

Solution

225a2+9b2+25c2-75ac-45ab-15bc=0

  215a2+3b2+5c2-15a5c-15a3b-3b5c=0 

  215a2+23b2+25c2-215a5c-215a3b-23b5c=0

15a-3b2+3b-5c2+5c-15a2=0

15a-3b=3b-5c=5c-15a=0

15a=3b=5c

  a1=b5=c3=k

   a=k, b=5k, c=3k

  a, c, b are in A.P.

  b, c, a are in A.P.

Asked in: JEE Main 2017 (02 Apr)

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