Question

Find the 4th term in the following sequence (n = 4)

a1 = 8

an = an-1 - 3

1) 2
2) -1
3) 1

Answer 1

this formula, doesn't rely on a product, relies on a "sum", or is namely an arithmetic sequence, aₙ₋₁ -3 is another way of saying, the value of the previous term minus 3, so it relies on the ordinal value of a term, so is an recursive formula, well, let's get it when n = 4.

`\begin{array}{ccll} order&term&value\\ \cline{1-3} 1&a_1&8\\ 2&a_2&a_(2-1)-3\\ &&a_1-3\\ &&8-3\\ &&5\\ 3&a_3&a_(3-1)-3\\ &&a_2-3\\ &&2\\ 4&a_4&a_(4-1)-3\\ &&a_3-3\\ &&2-3\\ &&-1 \end{array}`