Welcome to BdMO Online Forum. Let me answer it since nobody is doing so.
Suppose $m=2x+1$. The product becomes $\begin{align*}(m+4)(m-4) &=m^2-16\\
&=(2x+1)^2-16\\
&=4x^2+4x-15
\end{align*}$
Now setting $x=2$, we get $16+8-15=9$
Search found 1015 matches
- Sun Oct 09, 2016 10:14 am
- Forum: Junior Level
- Topic: Answer the question
- Replies: 2
- Views: 8156
- Sun Oct 09, 2016 10:02 am
- Forum: Higher Secondary Level
- Topic: external section formula
- Replies: 6
- Views: 9896
Re: external section formula
Yeah. Vector lengths are direction sensitive.
- Fri Oct 07, 2016 8:51 am
- Forum: Higher Secondary Level
- Topic: external section formula
- Replies: 6
- Views: 9896
Re: external section formula
Both of the formulae are correct. $C$ is not on the same end of $\vec{AB}$ in both proofs. That's why the formula changes.
Actually, there is no special formula called external section formula. It's just the internal section formula with one of the ratios being negative.
Actually, there is no special formula called external section formula. It's just the internal section formula with one of the ratios being negative.
- Sun Sep 25, 2016 10:26 pm
- Forum: News / Announcements
- Topic: About IOI.
- Replies: 1
- Views: 9622
Re: About IOI.
Ah, it's a very old question. Two IOIs have come and gone in the meantime. The next IOI, IOI '17, will be held in Tehran, Iran, during Jul 28-Aug 4.
A general tip- Google is usually the best place to find such info: https://goo.gl/U3ss0M
A general tip- Google is usually the best place to find such info: https://goo.gl/U3ss0M
- Sat Sep 24, 2016 12:58 pm
- Forum: Junior Level
- Topic: how can i solve this?
- Replies: 3
- Views: 4056
Re: how can i solve this?
রাস্তাসহ বাগানের ক্ষেত্রফল $60\times 40 = 2400$ বর্গমিটার রাস্তাছাড়া বাগানের দৈর্ঘ্য $60-2\times 2=56$ মিটার। (নিচের ছবিতে দেখ, বাগানের দৈর্ঘ্যের দিকে উভয় পাশে থেকে রাস্তার সমান দৈর্ঘ্য বাদ দিতে হবে।) একই যুক্তিতে রাস্তাছাড়া বাগানের প্রস্থ $40-2\times 2= 36$ মিটার অতএব, রাস্তাছাড়া বাগানের ক্ষেত্...
- Sat Sep 24, 2016 12:35 pm
- Forum: Higher Secondary Level
- Topic: Trigonometry
- Replies: 2
- Views: 7298
Re: Trigonometry
I remember the first problem from Neurone Onuronon. [Ah, nostalgia :") ] Anyway, here are your solutions: 1. Set $y=\sin x$. After some tedious calculations, it becomes apparent that $\cos y>\sin \left(\sqrt{1-y^2}\right)$. In other words, $\cos(\sin x) > \sin(\cos x)$. [You can also show it by comp...
- Sat Sep 24, 2016 11:08 am
- Forum: Site Support
- Topic: general Question
- Replies: 14
- Views: 29897
Re: general Question
Welcome to BdMO Online Forum. Here is how you can view your posts: Firstly, one of your posts must be approved by a moderator or an administrator. After that, 1) You'll see a tab named "view your posts" on the top-left corner of every page in this forum. Just click on this tab and you'll see a list ...
- Fri Sep 23, 2016 12:54 pm
- Forum: Combinatorics
- Topic: Combi Solution Writing Threadie
- Replies: 10
- Views: 13360
Re: Combi Solution Writing Threadie
Nice initiative. Go on!
- Fri Sep 23, 2016 12:51 pm
- Forum: Site Support
- Topic: Stuff on top
- Replies: 1
- Views: 10519
Re: Stuff on top
This is a persistent issue with forum's BBCodes. It is also responsible for the collapse of several blocks within the page. Unfortunately, there is nothing you can do to fix this problem apart from not using BBCodes. Here is a possible workaround: (1) Add some custom JavaScript runner extension to y...
- Fri Aug 12, 2016 12:53 pm
- Forum: Social Lounge
- Topic: A ques. about geo
- Replies: 2
- Views: 3219
Re: A ques. about geo
Most of the times, you don't need to prove those lemmas, since they are pretty much well known by now.
In general, if you are unsure whether you should prove a lemma or not, then just prove it. You have a lot of time in the major contests. Writing up a known proof or two won't hurt, will it?
In general, if you are unsure whether you should prove a lemma or not, then just prove it. You have a lot of time in the major contests. Writing up a known proof or two won't hurt, will it?