Question

find the sum of the arithmetic sequence. -10, -7, -4, -1, 2, 5, 8 select one: a. 11 b. -70 c. 0 d. -7

Answer 1

d -7

Explanation:

The sum of an arithmetic sequence Sn whose first and last terms are known may be expressed as

Sn = n/2(a + l)

where a and l are the first and last terms of the arithmetic sequence with n number of terms

Thus for the given sequence, the sum Sn is

S₇ = 7/2 (-10 + 8)

Since there are 7 terms in the sequence

= 3.5 * -2

= -7

Answer 2

This is an aritmetic series;
a=-10
d=-7--10
d=3
n= 7
Sum=
`(n)/(2)`(2a+(n-1)d)
Sum=
`(7)/(2) (2*(-10)+(7-1)3)`
sum=3.5(-20+18)
sum=3.5(-2)
sum=-7