Question

The common ratio of a G.P. is 3, and the last term is 486. If the sum of these terms be 728, find the first term.

Answer 1

Given: 

Common Ratio = 3 

Sum of GP = 728 

Sum of GP for n terms = \(\frac{a(r^n-1)}{r-1}\)

Last term say it be n 

∴ T_n = ar^{n - 1} 

⇒ 486 = a3^{n - 1}

∴ The first term is 2.