Since the dawn of time, two mysteries have plagued mathematicians: a) How do you find a centre of a 90º rotation? and b) What's the 45º set square for? Imagine my surprise when I discovered that each is the answer to the other! Some facts about the centre of rotation

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Posted in ninja maths.

"$y$," said the student, carelessly, "$=mx+c$," and before he knew it, his wrists and ankles were secured to the table and a laser was slowly, but extremely surely, cutting the table in two. The Mathematical Ninja continued the lesson. "I think you mean $y - y_1 = m(x-x_1)$," he said,

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Posted in logarithms.

A student asks: When I do inequalities with geometric series, I sometimes get my inequality sign the wrong way round - I can usually fudge it, but I'd like to be getting it right. OK, I confess, that student is me, circa 1995. And, in fact, I only figured it

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