Question

What is the answer to this question?

posted a picture for better understanding:)

Answer 1

5

Explanation:

Usually, the sequence is
`a_(1), a_(2), a_(3), a_(4), ..., a_(n)` where n is a postive number.

From the question,

`a_(n) = a_(n-1) - 5`

if n = 2 ;

`a_(2) = a_(1) - 5`

`a_(2) = 20 - 5 = 15\\`

Thus, we got
`a_(2) = 20`.

if n = 3 ;

`a_(3) = a_(2) - 5`

`a_(3) = 15 - 5 = 10`

Thus, we got
`a_(3) = 10`.

if n = 4 ;

`a_(4) = a_(3) - 5`

`a_(4) = 10 - 5 = 5`

Thus, we got
`a_(4) = 5`.

***There are many ways to solve this question

example:

`a_(n) = a_(n-1) - 5`

`a_(n) - a_(n-1) = - 5`

Substitute n with 2, 3, 4

Then, we will get 3 equations.

Sum them up;

We will get

`a_(4)-a_(3)+a_(3)-a_(2)+a_(2)-a_(1) = -15\\a_(4)-a_(1) = -15\\a_(4) = -15+20 = 5`