1)
Last term of our sum is 110, so answers C) and D) (infinite sums) are incorrect.
Now we can calculate first term (for n = 0) in A) and B):
A) [tex]-80\cdot 0=\boxed{0}[/tex]
B) [tex]-10+8\cdot0=-10+0=\boxed{-10}[/tex]
First term is -10 so B) is correct.
2)
We have:
+ 8 - 40 + 200 - 1000 + ... (different signs)
so there will be [tex](-5)^{...}[/tex] (answer A) or B) ).
Calculate first term:
A) [tex]8\cdot(-5)^{0+1}=8\cdot(-5)^1=\boxed{-40}[/tex]
B) [tex]8\cdot(-5)^{0}=8\cdot1=\boxed{8}[/tex]
Answer B)
