Answer:
too hard
Step-by-step explanation:
I think it would be the third idk tho I’m not good at math
For sake of convenience, reverse the series, then it would be:
21,19,17.....7
a=21, d = -2,
s(4) = 4/2 (21+15)
s(4)=2(36)
s(4) = 72
Answer:
Okay So I see you need to change 1/3 to a denominator of 6
You don't do anything to the -1/6
But to change the 1/3 you need to multiply 3 and 1 by two, which is 2/6
And the -1/6 stays the same