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Mathematics

If 5th, 8th and 11th terms of a G.P. are x, y and z respectively, then which one of the following is correct?

  1. y2 = x2z2

  2. y2 = x2 + z2

  3. y2 = xz

  4. xyz = 1

G.P.

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Answer

Let first term of G.P. be a and common ratio be r.

Given,

5th term = x

x = ar5 - 1

x = ar4

8th term = y

y = ar8 - 1

y = ar7

11th term = z

z = ar11 - 1

z = ar10

Substituting value of y in L.H.S. of y2 = xz

⇒ y2

⇒ (ar7)2

⇒ (a2r14)

Substituting value of x and z in R.H.S. of y2 = xz

⇒ xz

⇒ ar4 × ar10

⇒ a2r14.

Since, R.H.S. = L.H.S.

Hence proved, that y2 = xz.

Hence, option 3 is the correct option.

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