Verified Answer :

a2 = a1 r 
a2 = 10
.5 = 5 
a3 = a2 r 
a3 = 5
.5 = 2.5 
a4 = a3 r 
a4 = 2.5
.5 = 1.25 

the answer is 1.25

Answer

Find out the the value of the fourth term in a geometric sequence for  which

\(a_{1} = 10\ and\ r =0.5\)

To proof

The formula for the general term for each geometric sequence is

\(a_{n} = a_{1} r^{n-1}\)

where

\(a_{1} = first\ term,\ r = common\ ratio\)

Put n= 4

\(a_{4} = 10\times(0.5)^{4-1}\)

\(a_{4} = 10\times(0.5)^{3}\)

\(a_{4} = 10\times0.125\)

Solving

\(a_{4} = 1.25\)

The value of the fourth term in a geometric sequence is 1.25 .

Hence proved