waecmaths question:
Find the number of terms in the Arithmetic Progression (A.P) 2, –9, –20, …. –141
Option A:
11
Option B:
12
Option C:
13
Option D:
14
waecmaths solution:
$\begin{align} & a=2 \\ & d=-11 \\ & {{T}_{n}}=a+(n-1)d \\ & -141=2+(n-1)(-11) \\ & -141=13-11n \\ & 11n=154 \\ & n=14 \\\end{align}$
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