Jambmaths question:
If the 9th term of an AP is fives times the 5th term, find the relationship between a and d
Option A:
2a + d = 0
Option B:
3a +5d = 0
Option C:
a + 3d = 0
Option D:
a + 2d = 0
Jamb Maths Solution:
$\begin{align} & {{T}_{9}}=a+8d----(i) \\ & {{T}_{5}}=a+4d----(ii) \\ & {{T}_{9}}=5{{T}_{5}}=5(a+4d) \\ & \text{Equating (i) and (iii)} \\ & {{T}_{9}}=5a+20d---(iii) \\ & 5a+20d=a+8d \\ & 4a+12d=0 \\ & a+3d=0 \\\end{align}$
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