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Q9 (CISF/2019) Science & Technology › Basic Science (Physics, Chemistry, Biology)

If the third term of a GP is 4, then the product of first five terms of the GP is

Explanation

In a Geometric Progression (GP), let the first term be a and the common ratio be r. The general term is given by Tn = arn-1.

According to the question, the third term (T3) is 4:
T3 = ar3-1 = ar2 = 4

The product of the first five terms is calculated as:
Product = T1 × T2 × T3 × T4 × T5
Product = a × (ar) × (ar2) × (ar3) × (ar4)
Product = a(1+1+1+1+1) × r(0+1+2+3+4)
Product = a5r10

This expression can be rewritten as:
Product = (ar2)5

Substituting the value of ar2 = 4 from the given information:
Product = 45

Thus, the product of the first five terms is 45, which corresponds to option C.

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