Posted in arithmetic, ask uncle colin

Dear Uncle Colin, How would you find $\sqrt[4]{923521}$ without a calculator? -- Some Quite Recherché Technique Hi, SQRT! I have a few possible techniques here. The first is "do some clever stuff with logarithms", the second is "do some clever stuff with known squares" and the last is "do some

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Posted in podcasts

In this episode of Wrong, But Useful1: We're joined by @ajk_44, who is Alison Kiddle from NRICH in real life. We ask Alison: how long has NRICH been going? How do you tell which problems you've covered before? Colin's number of the podcast is 13,532,396,179 (he mistakenly calls it quadrillions

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Posted in exam technique, gcse

I imagine, if one put one's mind to it, one could acquire copies of this year's paper online - however, many schools plan to use it as a mock for next year's candidates. In view of that, and at the request of my top-secret source, I'm not sharing the actual

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Posted in calculus

Dear Uncle Colin, I've been asked to solve Chebyshev's equation using a series expansion: $(1-x)\diffn{2}{y}{x} - x\dydx + p^2 y = 0$ assuming $y=C_0 + C_1 x + C_2 x^2 + ...$. I end up with the relation $C_{N+2} = \frac{C_N \left(N^2 -p^2\right)}{(N+2)(N+1)}$, but the given answer has a +

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Posted in dialogue

This is a rolling update post for responses to this morning's post. The Admirable Adam Atkinson has emailed to suggest an answer I hadn't considered: 100. "I could imagine many programming languages would say 100. You start with the first term, 100. discover that the "next" number, 101, is outside

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Posted in dialogue

"Counting is hard. This is what I keep saying." - @realityminus3 It all stemmed from an arithmetic series problem with a known sum, but an unknown number of terms. As these things are prone to do, it led to a quadratic equation; as those things are prone to do, that

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Posted in ask uncle colin, complex numbers

Dear Uncle Colin, I've been given $u = (2\sqrt{3} - 2\i)^6$ and been told to express it in polar form. I've got as far as $u=54 -2\i^6$, but don't know where to take it from there! - Not A Problem I'm Expecting to Resolve Hello, NAPIER, and thanks for your

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Posted in proof

Someone recently asked me where I get enough ideas for blog posts that I can keep up such a 'prolific' schedule. (Two posts a week? Prolific? If you say so.) The answer is straightforward: Twitter Reddit One reliable source of interesting stuff is @WWMGT - What Would Martin Gardner Tweet?

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Posted in ask uncle colin, complex numbers, quadratics

Dear Uncle Colin, I'm told that $z=i$ is a solution to the complex quadratic $z^2 + wz + (1+i)=0$, and need to find $w$. I've tried the quadratic formula and completing the square, but neither of those seem to work! How do I solve it? - Don't Even Start Contemplating

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Posted in algebra

It turns out I was wrong: there is something worse than spurious pseudocontext. It's pseudocontext so creepy it made me throw up a little bit: This is from 1779: a time when puzzles were written in poetry, solutions were assumed to be integers and answers could be a bit creepy...

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