Question

I NEED HELP PLEASE THANKS! :) Find the seventh partial sum of 13, 22, 31, 40, ...

9
67
106
280

Answer 1

280

Explanation:

the 7th number is

Answer 2

Explanation:

Arithmetic sequence

First term a = 13

Common difference = 2nd term - first term

= 22 - 13

d = 9

`a_(n)= a + (n-1)d\\\\a_(7)= 13 + 6*9`

= 13 + 54

= 67

Sum of 7 terms =
`(n)/(2)(2a + (n-1)d)\\\\`

=
`(7)/(2)(2*13+6*9)\\`

=
`(7)/(2)(26+54)\\`

=
`(7)/(2)*80\\`

= 7 *40

= 280