Question

Given a term and the common difference, find the explicit formula. 8. a(19) = 135 d = 15

Answer 1

The explicit formula is a(n) = 15(n – 10)

Solution:

Given, a term a(19) = 135 and common difference d = 15

We have to find the explicit formula.

Now, we know that, a(n) = a + (n – 1)d where a(n) is nth term, a is first term, d is common difference,

So, for a(19)  

$\begin{array}{l}{\rightarrow a(19)=a+(19-1) 15} \\\\ {\rightarrow 135=a+18 \times 15} \\\\ {\rightarrow a=135-270} \\\\ {\rightarrow a=-135}\end{array}$

Now, we know that, an explicit formula is an expression for finding the nth term,  

So, in our problem, expression for finding nth term is a + (n – 1)d  

$\begin{array}{l}{\rightarrow-135+(n-1) 15} \\\\ {\rightarrow-135+15 n-15} \\\\ {\rightarrow 15 n-150} \\\\ {\rightarrow 15(n-10)}\end{array}$

Hence, the explicit formula is a(n) = 15(n – 10).