Asked by Isaac

How do I do this
Need details solution to follow up

prove that cos(a)+cos(a+b)+cos(a+2b)+....+cos(a+(n-1)b)={cos(a+((n-1)/2)bsin(nB/2)}/½sinb
for all N£N
Answered by oobleck
Hmmm. It's not even true for n=2, so I think something's wrong.
Answered by Isaac
How is it not true can you explain?
Answered by oobleck
geez - plug in n=2 and the equation generated is not true.
Answered by Isaac
This is part of an IMO question which I can't solve
Answered by oobleck
A question cannot be false. Apparently the identity they proposed is not true.
Take a look at what happens when
n=1: cos(a) = 2cos(a - b/2)sin(b/2)/sin(b)
n=2: cos(a) + cos(a+b) = 2cos(a + b/2)sin(b)/sin(b)
clearly neither of those is an identity.
Answered by oobleck
You can find answers to past IMO's online. They really are quite difficult. Maybe you should start with the MAA's AHSME, which is the gateway to the IMO. It's kind of the next step up from the SAT math area exams. I got 800 on each of those, and felt pretty competent, but blew it royally on the AHSME, even though I was top in my high school for three years running.

To tell you the truth, I have only tried a few IMO problems. They really require some sophistication and out-of-the-box thinking. If you finally get past the IMO, you can move on to the Putnam exam, given to college students. Two sets of six questions, each three hours. I got 11 out of 120 points, which is about average!
Answered by Isaac
Wow.......thanks sir obleck
Answered by Isaac
You're the best thanks for the info
Answered by Isaac
Can you give me a link to download

MAA's AHSME book??
Answered by oobleck
not off the top of my head, but google can
Answered by Isaac
Okay will search....but I would need a tutor with IMO experience to guide me through it.........can I be posting them here for you to help me... provide Link and key areas for me ??
Answered by oobleck
just look up some past IMO solutions. They explain how to solve the problems. I doubt I will be of much help on these questions.
There are no AI answers yet. The ability to request AI answers is coming soon!