:: Bài Khảo Cứu:

- Câu Chuyện Về Charles Darwin Và Thuyết Tiến Hóa (Trần Hồng Văn)

- Stephen Hawking, người từng khước từ một bản án tử hình (Mạnh Kim)

....

:: Bài Tập Hình Kỳ Sau:

Bài 49:

Trên đường tròn tâm O bán kính R lấy 6 điểm D, E, F, G, H, K theo thứ tự, sao cho DE = FG = HK = R. Các đường thẳng KD cắt EF tại A, EF cắt GH tại B, GH cắt KD tại C. Chứng minh: OA . BC = OB . CA = OC . AB.

:: Toán Quốc Tế:

(Hình Học)

IMO năm: 10, 08, 07, 06, 05, 04, 03, 02, 01, 00, 97, 87, 85, 75, 65

Các đề thi (bắt đầu lần thứ nhất):

http://www.imo-official.org/year_info.aspx?year=1959

http://www.artofproblemsolving.com/Wiki/index.php/IMO_Problems_and_Solutions

http://www.mat.itu.edu.tr/gungor/IMO/www.kalva.demon.co.uk/imo.html

:: Đố Vui (22):

The Guido Mosaics Puzzle (by Sam Loyd)

Cut the mosaic into parts which will form two squares.

It is not generally known that the celebrated piece of Venetian mosaic by Domenichino, known as the Guiđo collection of Roman heads, was originally divided into two square groups, discovered at different periods. They were brought together and restored to what is supposed to be their correct form, in 1671. Apparently by accident it was discovered that each of the two squares consisted of pieces which would fit together into one 5 x 5 piece as shown.

It is a pretty puzzle, and as many puzzles, like mathematical propositions, can be worked backward to advantage at times, we will reverse the problem and ask you to divide the large square into the fewest number of pieces which can be refitted into two squares.

This puzzle differs from the Pythagorean principle of cutting lines on the bias. We know that two squares can be divided by diagonal lines to produce one larger square, and vice versa, but in this puzzle we must cut on the lines only, so as not to destroy the heads. It may also be mentioned, incidentally, that students who have mastered the Pythagorean problem will not find much difficulty in discovering how many heads there must be in the smaller squares.

Problems of this kind, which call for the "best" answer in the "fewest number of pieces," offer great scope for cleverness. In this problem the best solution does not destroy any heads or turn any of them upside down. (Mathematical Puzzles of SAM LOYD, Martin Gardner)

GIẢI ĐÁP ĐỐ VUI KỲ TRƯỚC:

Đố Vui (21) How old is the mother? (by Sam Loyd)

The mother's age is 29 years and 2 months. Tommy's age is 5 years and 10 months, and the father is 35 years old.

ĐỐ VUI CÁC KỲ TRƯỚC