Question

Find the sum. -85+ (-81) + (-77)+...+31 + 35

Answer 1

Answer:

The sum of all the terms is -775.

Step-by-step explanation:

This appears to be an arithmetic sequence, with a common difference of 4.

The problem is, we don't know how many terms there are!

To find this, use the following formula:

last number = first number + (n - 1) * difference

In this case:

35 = -85 + (n - 1) * 4

35 = -85 + 4n - 4

4n = 124

n = 31

This means there are 31 terms in this sequence.

Now, for the sum. Use the following formula:

n(first number + last number), take this product and divide it by 2.

In this case:

31(-85 + 35) = -1550 / 2 = -775