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A nice coordinate geometry problem (suitable for Form 7 pure)

十月 28, 2009

Let A(a, a^3 + pa + q) be a point on the curve C:  y = x^3 + px + q. 閱覽全文 »

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For my IMO Students (Basic and Advanced)

十月 28, 2009

Here is good problem for my IMO students.

Given a real number R > 0. Find the greatest area of triangle ABC with circum-radius R.

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For my Form 7 Pure students: A proof of the Rational Root Theorem

十月 19, 2009

Let f(x) = a_nx^n + a_{n-1}x^{n-1} + \dots + a_1x + a_0 \in \mathbb{Z}[x]. Suppose p/q, where \gcd(p, q) = 1 is a rational root.

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To my Form 7 students: I am impressed!

十月 15, 2009

Just finished my CB class tonight and I am impressed by two students. They both expressed interests in the following problem:

Suppose p(x) is a polynomial of degree n. Suppose further that

(i) p(x) - p(x - 1) = x^{100} for all x, and

(ii) p(1) = 1.

Find the leading coefficient of p(x) and the degree of p(x).

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Selected solutions for my F7 Pure (Polynomials)

十月 3, 2009

Book 2, pg 14. (00IQ12)(c)
(i) Let y = x^2, then we have ay^2 – by + a.
Considering the discriminant yields: b^2 – 4a^2 > 0. Therefore, it has two distinct roots: \alpha, \beta. If they are both positive, then we are done. Otherwise, they must be both negative since \alpha \beta = a/a = 1. (Note a \not = 0 since ab > 0.)
Suppose \alpha, \beta < 0. Then we have x = \pm i \sqrt{|\alpha|}, \pm i \sqrt{|\beta|}.

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Selected solutions for my A.maths students (theory of quadratics)

十月 2, 2009

Notes L1b, Page 14.

Given \alpha, \beta are roots of x^2 + (1 - x)^2 - m. Suppose |\alpha| = |2\beta|, determine the values of m.

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IMO phase II training Homework Solution

九月 27, 2009

Here is my solution to the following problem given in IMO phase II training for the basic group:

Problem(1): Find all positive integer solutions to: x^3 - y^3 = xy + 61.

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Challenging problem in Linear Algebra

八月 19, 2009

Let \mathcal{M} = \left\{ \begin{pmatrix} a & -b \\b & a \end{pmatrix} \, | \, a, b, \in \mathbb{R} \right\}.

Solve the following matrix equation X^4 + X^2 + I = 0 where X \in \mathcal{M}.

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Answers to Linear Algebra Concept Check

八月 19, 2009

Let (E) be the following system:

a_{11}x + a_{12}y + a_{13}z = b_1\\a_{21}x + a_{22}y + a_{23}z = b_2 \\a_{31}x + a_{32}y + a_{33}z = b_3

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Mental exercises for my Pure Complex Class (1)

八月 19, 2009

Dear Students,

Please avoid as much calculations as possible. In ideal situation, you should not do any calculation at all.

Problem 1
Let z = 3 + 4i be a complex number.
(a) Find Re(z).
(b) Find Im(z).
(c) Find \overline{z}.
(d) Find |z|^2.
(e) Find Re(1/z).
(f) What is z \overline{z}?
(g) Suppose z = re^{i \theta}, write r in terms of z

Problem 2
(a) Write z = i in the form re^{i \theta}.
(b) Find the two square roots of i and represent the two square roots on the Gaussian Plane.

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