Class 11 Maths Sequences Series | Geometric Mean |

**Geometric Mean**

** **The geometric mean of two positive numbers a and b is the number √ab . Therefore, the geometric mean of 2 and 8 is 4. We observe that the three numbers 2,4,8 are consecutive terms of a G.P. This leads to a generalization of the concept of geometric means of two numbers.

Given any two positive numbers a and b, we can insert as many numbers as we like between them to make the resulting sequence in a G.P.

**Numerical**: Insert three numbers between 1 and 256 so that the resulting sequence is a G.P.

**Solution**: Let G1, G2,G3 be three numbers between 1 and 256 such that 1, G1,G2,G3 ,256 is a G.P. – (i)

We can rewrite this GP as a, ar, ar^{2}, ar^{3}, ar^{4} --(ii)

Comparing (i) & (ii), we get a=1 & ar^{4} = 256 or r = ± 4

For *r *= 4, we have G1 = *ar *= 4,

G2 = *ar*^{2} = 16,

G3 = *ar*^{3} = 64

Similarly, for *r *= – 4, numbers are – 4,16 and – 64.

Hence, we can insert 4, 16, 64 or – 4, 16 and – 64 between 1 and 256 so that the resulting sequences are in G.P.

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