Question

Find the sum of the first 12 terms of the sequence

1, -4, -9, -14, . . .

Answer 1

okay I'll show you a cool way of doing this

Answer 2

use the equation
a+(n-1)d
where a= first term (1 here)
d= difference between two elements (which is -5 here)

Answer 3

so we get
6-5n

Answer 4

and name that value as x=6-5n

Answer 5

to get the sum, use the equation
s=n(a+x)/2

Answer 6

where n=12
a=1 and x=6-5(12)

Answer 7

hope this helped

Answer 8

It did, thank you!

Answer 9

you are welcome