The seconds term of a geometric series is 4 whi... - JAMB Mathematics 2011 Question

T₂ = 4, T₄ = 16

T_x = ar^n-1

T₂ = ar^2-1 = 4 i.e. ar³ = 16, i.e. ar = 4

T₄ = ar^4-1

therefore, (\frac{T_4}{T_r}) = (\frac{ar^3}{ar}) = (\frac{16}{4})

r² = 4 and r = 2

but ar = 4

a = (\frac{4}{r}) = (\frac{4}{2})

a = 2

Sⁿ = (\frac{a(r^n - 1)}{r - 1})

S⁵ = (\frac{2(2^5 - 1)}{2 - 1})

= (\frac{2(32 - 1)}{2 - 1})

= 2(31)

= 62