Hanoi2an

Like Sakan7's method, we have a99 = 9, a4 = 4. Now we sum them up: a100 = a99 - a98 a99 = a98 - a97 a98 = a97 - a96 a97 = a96 - a95 ...................... ...................... a3 = a2 - a1 a2 = a2 a1 = a1 __________________ a100 + a99 + a98 + a97 + .... a5 + a4 + a3 + a2 + a1 = (a99 - a98) + (a98 - a97) + (a97 - a96) + ..... + (a4 - a3) + (a3 - a2) + (a2 - a1) + a2 + a1 = a99 + a2 = 9 + 4 = 13 I think n >= 1, n is a natural number. You did not give us the condition of n. n might be 0 and, in this case, it could give us an other result. if n >= 0 a2 = a1 - a0 => a0 = a1 - a2 = -5 - 4 = -9 and the sum of the first 100 terms would be counted from a0 to a99 a99 + a98 + a97 + ..... + a1 + a0 = (a98 - a97) + (a97 - a96) + .... + (a4 - a3) + (a3 - a2) + (a2 - a1) + (a1 - a0) + a1 + a0 = a98 + a1 = 4 + (-5) = -1

Hi! I'm from Vietnam. I'm preparing for the TOEFL test, too. I'd love to join you guys, if there's a vacant seat for me :)

hey guys! I have 2 Skype ID, CONTACT DETAILS DELETED BY MODERATOR. Please use Test Magic messaging system. Let's speak English out loud!

I want to take a TOEFL test next summer. I'm looking for people who will take it at that time. This is one note I wrote in my Facebook, I'm gonna post it here so you can read it: Hi guys! I want to create a TOEFL & IELTS speaking group on skype. If you wanna join this group (group N1), read this: 1. The group consists of 4-6 members whose level is upper-intermediate or higher. (For now, there're 2 members. When I have 3 or 4 more, we'll act.) 2. You have free time. We talk once a week on Sunday or Saturday at 20:00 in Vietnam. We continue until August or September next year. If sometimes you're busy, you need to inform us before Friday. For more than 2 times being absent without no word, you'll be removed from the group. 3. Topics we talk about are those used in the TOEFL or IELTS exams. I'll send you a topic each week or we all will agree to what topics to be used. You will also suggest your ideas. You must take responsibility. 4. For guys who haven't given me any information, you need to give me these: 1- Name: (in latin) 2- Skype: 3- Email address: 4- Facebook: 5- Country, city and time zone: 6- Level of English: Free time and English level are fixed as Sat./Sun. and upper-inter./higher. You can find my Facebook using the username hocnoitienganh. This is not my Skype ID or email, it's just the username on Facebook. When you add me to your FB, you must also send me a private message including this necessary information. (Do NOT post your contact information here - in this forum!) 5. If you wanna join this group, please comment on this note to register (of course this group is for upper-inter. or higher level). Being a member of this group (group 1), you must take responsibility for it. (You'll find this note when you're already in my list of friends) ---------------- If someone whose level meets the requirement doesn't wanna join this group, he/she can still talk in the previous group (let's call it group 2). The group N2 talk on Sunday if the first one talk on Saturday or Saturday if the first - Sunday. ---------------------------------------- Please look for my facebook and do what I say above. Do not post your information here because they may delete this thread! Thank you guys!

Hi guys! I'm planning to take a TOEFL test next year too. So if you wanna, you can go to my facebook with the username 'hocnoitiengAnh'. I can't post the full link to my FB or my Skype here because it would break the rule of this forum. Thank you!