Question

Find the 21st term in the followingarithmetic sequence :-1, -3, -5, -7,

Answer 1

Arithmetic sequence formula

`a_n=a_1+(n-1)d`

where

• aₙ: the nᵗʰ term in the sequence

,

• a₁: the first term in the sequence

,

• d: the common difference between terms

In this case, the first term is a₁ = -1.

The common difference is obtained by subtracting two consecutive terms, as follows:

`d=-3-(-1)=-2`

To find the 21st term, we need to substitute n = 21. Using this value of n and the previously found values of the other constants, we get:

`\begin{gathered} a_(21)=-1+(21-1)(-2) \\ a_(21)=-1+(20)(-2) \\ a_(21)=-1-40 \\ a_(21)=-41 \end{gathered}`