PLEASE ANSWER THIS : 40 POINTS
2 answers:
the answer is -50 if you would like the work pls contact me personally
Answer:
S10 = -50
Step-by-step explanation:
an = a1 +d(n-1) is the formula for an arithmetic series
The 4th term is
4 =a1 + d(4-1)
4 = a1 + 3d
The 8th term is
-20 =a1 + d(8-1)
-20 = a1 + 7d
Subtract these two equations
-20 = a1 + 7d
-(4 = a1 + 3d)
--------------------------
Distribute the subtraction sign
-20 = a1 + 7d
-4 =- a1 - 3d
--------------------------
-24 = 4d
Divide by 4
-24/4 = 4d/4
-6 =d
Now we can calculate a1
4 = a1 + 3d
4 = a1 +3(-6)
4 = a1 -18
Add 18 to each side
4+18 =a1
a1 =22
an = 22 -6(n-1)
The sum is found by using
Sn = n/2 (a1+an)
We need the 10th term
a10 = 22 -6(10-1)
a10 = 22 -6*9
=22 -54
=-32
Sn = 10/2 (22-32)
= 5(-10)
-50
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