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## liliy find the value of the sum: summation j=0 until j=8; (1+(-1)^j)) one year ago one year ago

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1. KonradZuse

plug it in?

2. KonradZuse

$\sum_{0}^{8} (1+(-1)^j)$

3. liliy

we need to use the formula for progresion. but i dont know how. bec the formula is : n(a sub 1 +a sub n) /2

4. liliy

but is the zero considered ":a sub 1 or a sub 0,?"

5. KonradZuse

Idk why you need a formula... unless I'm missing something.. You should be able to just plug in and get your answer...

6. liliy

the instructions say use th formla

7. KonradZuse

n should be 8, but not too sure about a, maybe the current #? I haven't done this in awhile :P.

8. liliy

wait, without the formula the answer is 10?

9. KonradZuse

yes. correct!e

10. liliy

hmm so this formula is not giving me that answer. no matter which numbers i put in.