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Mathematics
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Mathematics
A few useful notions:
- the angle between two vectors A and B is given by the formula
cos(theta) = <A, B> / (|A| * |B|);
where <A, B> is the scalar product of A and B.
Neither A nor B may be null.
- the scalar product of (a, b, c) and (x, y, z) is (ax, by, cz).
- the projection of B on A is the following vector:
(<A, B> / <A, A>) * A.
A must not be null.
- the vector product of (a, b, c) and (x, y, z) is (bz-cy, cx-az, ay-bx).
- the logarithm in base b of x is ln(x) / ln(b),
or log(x) / log(b),
where ln is the natural logarithm and log is the base 10 logarithm.
Slide Rule - Proportion, Percentage, Squares And Square Roots (1944)
March 8, 2025
A 1944 film (20m17s) on how to use the slide rule to calculate
squares, square roots, etc.
Math Smarts: Nurture Not Nature
February 20, 2001
This article explains that mathematical abilities are innate
in humans, and thus that anybody can learn them successfully.
Most people who find math problems difficult, Devlin said,
haven't mastered the ability to trick their minds into thinking
of math as TV, to fool their brains into making abstract objects
seem real.
HAKMEM
January 12, 2001
Work reported in this 1972 document was conducted at the
Artificial Intelligence Laboratory, a Massachusetts Institute
of Technology research program supported in part by the
Advanced Research Projects Agency of the Department of Defense.
It contains some little known data which may be of interest to
computer hackers.
(Link updated on March 22nd, 2010.)
Astronomy
Cutting the space budget really restores my faith in humanity. It
eliminates dreams, goals, and ideals and lets us get straight to the
business of hate, debauchery, and self-annihilation.
-- Johnny Hart
Gomez's Hamburger
August 10, 2002
This page from the Astronomy Picture of the Day web site
shows a photograph of a mouthwatering space hamburger,
which is named Gomez's Hamburger.
(This would make a great restaurant name, by the way.)
Changing the Earth's orbit
February 5, 2001
Some astronomers are proposing that we push the Earth away
from the Sun some day, so as to compensate for the increasing
heat that will be emitted by our star during the next
billion years.
The proposed technique would use the gravitation of a
100 kilometer asteroid.
It would allow us to move other planets, like Mars, into
a position more favorable to the development of life.
Astronomy Picture of the Day
December 20, 1998
This NASA site shows
a different image or photograph of the universe each day.
Star Gazer
April 1, 1998
The world's first and only weekly TV series
on naked-eye astronomy.
This series can be seen on PBS throughout
North America since 1976.
International Dark-Sky Association
March 8, 1998
An association that promotes the reduction of light pollution
which prevents people in cities from seeing the stars at night.
If you doubted that there was an association for Everything,
you are now confounded.
Amateur astronomy should be accessible to all,
and it is a shame that inefficient lighting in many cities
prevents people from admiring the spectacle of our Universe.
Skepticism
"To teach superstitions as truth is a most terrible thing."
-- Hypatia of Alexandria
Skeptic's Dictionary
November 12, 1998
This site gives the skeptical point of view about a great number
of obscure subjects, like Edgar Cayce, facilitated communication,
UFOs, etc.
The Quebec Skeptics Association
October 6, 1998
This is one of the largest skeptics clubs
in the world and one that is very involved in educating the public.
This club promotes rational and critical thought.
The Club is also offering 750'000$CAN to anyone who can
scientifically demonstrate a paranormal phenomenon...
James Randi Educational Foundation
December 7, 1997
Magician James "The Amazing" Randi
has created a foundation that offers
more than 1,100,000$ to anyone who can demonstrate
a paranormal phenomenon in a scientific test.
Isn't it amazing that certain people are
absolutely convinced that they have supernatural powers
but that none of them seems interested in collecting such
an amount of money?
Food for thought...
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