## anonymous one year ago Write the sum using summation notation, assuming the suggested pattern continues. -9 - 3 + 3 + 9 + ... + 81

1. anonymous

@surjithayer

2. anonymous

it is an A.P. a=-9 d=-3-(-9)=-3+9=6 find n by the the formula $l=a+(n-1)d$ can you find n l=81

3. anonymous

are you here?

4. anonymous

5. anonymous

these are answer options find n

6. anonymous

i did A @surjithayer

7. anonymous

i want to know how? can you show me ?

8. anonymous

@surjithayer i guessed im sry i suck at math

9. anonymous

ok.

10. anonymous

81=-9+(n-1)*6 81+9=(n-1)6 $\frac{ 90 }{ 6 }=n-1$ n-1=15 n=15+1=16

11. anonymous

you got it.

12. anonymous

but on all of them n=0

13. anonymous

wait is it d?

14. anonymous

that means there are 16 terms for n=0,1,2,...,15

15. anonymous

here for A ,n=0 a1=-9 a2=-9+6*1=-3 a3=-9+6*2=3 ..... a16=-9+6*15=81

16. anonymous

I said A in the first place @surjithayer

17. anonymous

A is correct. as i have shown.

18. dan815

would you like to see how sum of arithmetic series formula comes

19. anonymous

could u show me on this one? Write the sum using summation notation, assuming the suggested pattern continues. 5 - 15 + 45 - 135 + ...

20. anonymous

it is a G.P. can you find r?

21. anonymous

what is gp, i need it in summation notation

22. anonymous

gp means geometric progression

23. anonymous

for that you have to find r(common ratio)

24. anonymous

$r=\frac{ t _{n} }{ t _{n-1} }$ to be precise 2nd term/1st term

25. anonymous

@surjithayer what one did u get as the answer

26. anonymous

$r=\frac{ 45 }{ -15 }=?$

27. anonymous

$r=\frac{ -15 }{ 5 }=\frac{ 45 }{ -15 }=?$

28. anonymous

@surjithayer its b right?

29. anonymous

r=-3 B is correct.