# Algebra

posted by Jess

I have a few problems I need some help with.

The first is Evaluate the sum.
1. There is an E like symbol on the top is 10 on the bottom n=1 and to the right (7-2n)

2. The next question is find a10 for an arithmetic sequence with a1=6 and d=10

3. Find the number of terms in the series and then find the sum. Evaluate the sum.
16+23+30+37+44+.....+93

1. Steve

1. What you have is an arithmetic sequence where a=3 and d=-2
So, S10, the sum of the first 10 terms, is

S10 = 10/2 (2*3 + 9(-2)) = -60

same way for #2

3. looking at the terms, the difference is 7. Dividing the range of terms, we see that (93-16)/7 = 11

So, 7 is added to 16 11 times to get to 93. So, there are 12 terms.
Now find the sum the same way, using a=16,d=7,n=12

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