How do I find n (when tn = -20) in the arithmetic series 5 and 1/3, 5, 4 and 2/3... using the formula $${\mathtt{tn}} = {\mathtt{a}}{\mathtt{\,\small\textbf+\,}}\left({\mathtt{n}}{\mathtt{\,-\,}}{\mathtt{1}}\right){\mathtt{\,\times\,}}{\mathtt{d}}$$
+130516 I assume you might be wanting to know which term of the series = - 20....if so, we have......
-20 = [5 + 1/3] + (-1/3) (n-1) simplify
-20 = 16/3 + (-1/3)(n-1) multiply through by 3
-60 = 16 - 1(n - 1) subtract 16 from both sides
-76 = -n + 1 subtract 1 from both sides
-77 = -n multiply through by -1
77 = n
It will be the 77th term....!!!!
+130516 I assume you might be wanting to know which term of the series = - 20....if so, we have......
-20 = [5 + 1/3] + (-1/3) (n-1) simplify
-20 = 16/3 + (-1/3)(n-1) multiply through by 3
-60 = 16 - 1(n - 1) subtract 16 from both sides
-76 = -n + 1 subtract 1 from both sides
-77 = -n multiply through by -1
77 = n
It will be the 77th term....!!!!
