Question 19

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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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