Given: second term of a GP is 24 and its fifth term is 81.
To find: sum of first five terms of the G.P.
ar = 24 & ar4 = 81
dividing these two terms we get:
\(\Rightarrow\) \(\frac{ar^4}{ar} = \frac{81}{24}\)
\(\Rightarrow\) r3 = \(\frac{27}{8}\)
Taking cube root on both the sides we get,
⇒ r = \(\frac{3}{2}\)
Substituting this value of r in ar = 24 we get
a = 24/(3/2) = (24 × 2)/3 = 16
∴ Sum of first Five terms of a G.P. = a(rn - 1)/(r - 1)
