# Blog Archives

## CGMO-2012 (China Girls Math Olympiad 2012) Problem-3

Find all pairs of integers satisfying: there exists an integer such that is divisible by for all positive integers

## IMO 2012 problems

This year IMO problems !!!!

**Problem 1 :
**

Given triangle the point is the centre of the excircle opposite the vertex This excircle is tangent to the side at , and to the lines and at and , respectively. The lines and meet at , and the lines and meet at Let be the point of intersection of the lines and , and let be the point of intersection of the lines and Prove that is the midpoint of .

**Problem 2 :**

Let be an integer, and let be positive real numbers such that Prove that

**Problem 3 :**

The *liar’s guessing game* is a game played between two players and . The rules of the game depend on two positive integers and which are known to both players.

At the start of the game chooses integers and with Player keeps secret, and truthfully tells to player . Player now tries to obtain information about by asking player questions as follows: each question consists of specifying an arbitrary set of positive integers (possibly one specified in some previous question), and asking whether belongs to . Player may ask as many questions as he wishes. After each question, player must immediately answer it with [i]yes[/i] or [i]no[/i], but is allowed to lie as many times as she wants; the only restriction is that, among any consecutive answers, at least one answer must be truthful.

After has asked as many questions as he wants, he must specify a set of at most positive integers. If belongs to , then wins; otherwise, he loses. Prove that:

1. If then can guarantee a win. 2. For all sufficiently large , there exists an integer such that cannot guarantee a win.

**Problem 4 :**

Find all functions such that, for all integers that satisfy , the following equality holds:

** Problem 5 :**

Let be a triangle with , and let be the foot of the altitude from . Let be a point in the interior of the segment . Let be the point on the segment such that . Similarly, let be the point on the segment such that . Let be the point of intersection of and .

Show that .

**Problem 6 :**

Find all positive integers for which there exist non-negative integers such that

You may download the PDF version :

IMO 2012

Thank you and good luck for these delicious problems

## Infinite number of primes :)

In today’s post , I will present a very well known proof. What makes this proof especially appealing is that it is not too complex. Even so, it is very **powerful.** This theorem was first presented in Euclid’s Elements (Book IX, Proposition 20).

Theorem: **There are an infinite number of primes.**

Proof:

(1) Assume that there is only a finite number of primes.

(2) Then, there exists a prime p_{n} that is the largest prime.

(3) Let p_{1}, p_{2}, …, p_{n} be the list of all primes that exist.

(4) Let x = p_{1}*p_{2}*…*p_{n} + 1.

(5) By the fundamental theorem of arithmetic (see Theorem 3, here), we know there is at least one prime that divides x. Let us call this prime p*.

(6) But none of the primes p_{1} … p_{n} divide x since x ≡ 1 (mod p_{i}) for any of the primes p_{1} … p_{n}

(7) Therefore, we have a contradiction. We have a prime p* that is not in the complete list of primes.

(8) So, we reject our assumption in step#1 and conclude that there are an infinite number of primes that exist.

QED

## Bumper Problems

These are the set of 5 problems each of 5 marks

The person who get more than 20 points will get a mathematics book on any topic he want…

So try these beautiful problems to test your mathematics abilities and getting new things…

Ways by which you can answer :

I am adding a form in the end of this post , you can answer there ….

Note : You have give solution of your answer too..

**Problem 1)**

The bisectors of the angles and of the meet the sides

and at the points and , respectively.

Assuming that , determine the angle

**Problem 2)**

Given a and be point on side such that ,

, and

Find the value of

**Problem 3)**

If p and q are natural numbers so that

Prove that p is divisible by 1979 .

Problem 4)

Find highest degree n of 1991 for which 1991ⁿ divides the number :

**Problem 5)**

Let ƒ(n) denote the sum of the digits of n. Let N = 4444⁴⁴⁴⁴

Find ƒ(ƒ(ƒ(n))))

You can use these symbols to write solutions more conveniently

Mathematical Operators |
||||||||||||||||

∀ | ∁ | ∂ | ∃ | ∄ | ∅ | ∆ | ∇ | ∈ | ∉ | ∊ | ∋ | ∌ | ∍ | ∎ | ∏ | |

∐ | ∑ | − | ∓ | ∔ | ∕ | ∖ | ∗ | ∘ | ∙ | √ | ∛ | ∜ | ∝ | ∞ | ∟ | |

∠ | ∡ | ∢ | ∣ | ∤ | ∥ | ∦ | ∧ | ∨ | ∩ | ∪ | ∫ | ∬ | ∭ | ∮ | ∯ | |

∰ | ∱ | ∲ | ∳ | ∴ | ∵ | ∶ | ∷ | ∸ | ∹ | ∺ | ∻ | ∼ | ∽ | ∾ | ∿ | |

≀ | ≁ | ≂ | ≃ | ≄ | ≅ | ≆ | ≇ | ≈ | ≉ | ≊ | ≋ | ≌ | ≍ | ≎ | ≏ | |

≐ | ≑ | ≒ | ≓ | ≔ | ≕ | ≖ | ≗ | ≘ | ≙ | ≚ | ≛ | ≜ | ≝ | ≞ | ≟ | |

≠ | ≡ | ≢ | ≣ | ≤ | ≥ | ≦ | ≧ | ≨ | ≩ | ≪ | ≫ | ≬ | ≭ | ≮ | ≯ | |

≰ | ≱ | ≲ | ≳ | ≴ | ≵ | ≶ | ≷ | ≸ | ≹ | ≺ | ≻ | ≼ | ≽ | ≾ | ≿ | |

⊀ | ⊁ | ⊂ | ⊃ | ⊄ | ⊅ | ⊆ | ⊇ | ⊈ | ⊉ | ⊊ | ⊋ | ⊌ | ⊍ | ⊎ | ⊏ | |

⊐ | ⊑ | ⊒ | ⊓ | ⊔ | ⊕ | ⊖ | ⊗ | ⊘ | ⊙ | ⊚ | ⊛ | ⊜ | ⊝ | ⊞ | ⊟ | |

⊠ | ⊡ | ⊢ | ⊣ | ⊤ | ⊥ | ⊦ | ⊧ | ⊨ | ⊩ | ⊪ | ⊫ | ⊬ | ⊭ | ⊮ | ⊯ | |

⊰ | ⊱ | ⊲ | ⊳ | ⊴ | ⊵ | ⊶ | ⊷ | ⊸ | ⊹ | ⊺ | ⊻ | ⊼ | ⊽ | ⊾ | ⊿ | |

⋀ | ⋁ | ⋂ | ⋃ | ⋄ | ⋅ | ⋆ | ⋇ | ⋈ | ⋉ | ⋊ | ⋋ | ⋌ | ⋍ | ⋎ | ⋏ | |

⋐ | ⋑ | ⋒ | ⋓ | ⋔ | ⋕ | ⋖ | ⋗ | ⋘ | ⋙ | ⋚ | ⋛ | ⋜ | ⋝ | ⋞ | ⋟ | |

⋠ | ⋡ | ⋢ | ⋣ | ⋤ | ⋥ | ⋦ | ⋧ | ⋨ | ⋩ | ⋪ | ⋫ | ⋬ | ⋭ | ⋮ | ⋯ | |

⋰ | ⋱ | ⋲ | ⋳ | ⋴ | ⋵ | ⋶ | ⋷ | ⋸ | ⋹ | ⋺ | ⋻ | ⋼ | ⋽ | ⋾ | ⋿ | |

Exponents : ⁰ ¹ ² ³ ⁴ ⁵ ⁶ ⁷ ⁸ ⁹ ⁺ ⁻ ⁼ ⁽ ⁾ ₀ ₁ ₂ ₃ ₄ ₅ ₆ ₇ ₈ ₉ ₊ ₋ ₌ ₍ ₎ |

## Modular Arithmetic

**Modular arithmetic** is a notation and set of mathematics that were first introduced by Carl Friedrich Gauss. 🙂

The major insight is that equations can fruitfully be analyzed from the perspective of remainders. Standard equations use the ‘=’ sign. Modular arithmetic uses the ‘**≡**‘ sign. Two values that are ‘≡’ to each other are said to be congruent relative the modulus. In the case below, the modulus is 3. 🙂

Here’s an example of a modular equation:

7 ≡ 1 (mod 3).

By definition, this means that 3 divides 7 – 1.

**Definition 1**: a ≡ b (mod c) if and only if c divides a – b.

This definition tells us the following is true:

7 ≡ 1 ≡ 10 ≡ -2 (mod 3).

Now, one of the most interesting things about ‘≡’ is that it follows many of the same relations as ‘=’ . 🙂 🙂

**Notice 1**: For any value a,b,c,d,n where** a ≡ b (mod n) and c ≡ d (mod n): 🙂**

(a) **a + c ≡ b + d (mod n)**

** Proof :** We know that n divides (a + c) – (b + d) since this is equal to: (a -b) + (c – d).

(b) **a – c ≡ b – d (mod n)**

**Proof :** We know that n divides (a – c) – (b – d) since this is equal to: (a – b) – (c – d).

(c) **ac ≡ bd (mod n)**

**Proof :** We know that n divides ac – bd since this is equal to : c(a – b) + b(c – d).

(Q.E.D)

**Notice 2:** If **a ≡ b (mod n)** then:

(a)** a + c ≡ b + c (mod n)**

**Proof** : We know (a) since n divides a + c – (b + c) = a – b.

(b)** a – c ≡ b – c (mod n)**

** Proof** : We know (b) since n divides a – c – (b – c) = a – b.

(c) **ac ≡ bc (mod n)**

**Proof**: We know (c) since n divides ac – bc = c(a – b)

(Q.E.D)

**Corrolary 2.1**: **a ≡ d (mod n), b ≡ e (mod n), c ≡ f (mod n)**, then:

**a + b + c ≡ d + e + f mod n **

(1) We know that a + b ≡ d + e from above.

(2) We therefore know that (a + b) + c ≡ (d + e) + f.

(Q.E.D)

**Notice 3**: **a + b + c ≡ 0, a ≡ 0 (mod p), then b + c ≡ 0 (mod p).**

(1) a + b + c ≡ 0 (mod p) [Definition of ≡ ]

(2) b ≡ c (mod p) → a + b ≡ a + c (mod p) [See above]

(3) So, 0 ≡ a + b + c ≡ 0 + b + c ≡ b + c (mod p).

(Q.E.D)

I will cover modular arithmetic in depth 🙂 🙂

Today you must we wondering about its application ..

But after whole course You will surely love this topic

Thank you 🙂 🙂

If any doubts , then dont hesitate in asking Your doubts 🙂 🙂

I will surely love to solve your doubts

## Problem of the day !

We have started one more interesting feature of the blog

I will be posting problem of the day , and the best answer will be highly appreciated

If you win problem of the day for more than 4 times in a week then I will send you a mathematics very interesting E-Book

So here is Question 1 )

**QUESTION 1 )**

How many digits does the number 2^{1000} contain?

NOTE :

You have to give solution of your answer too