# Author: Colin

## Wrong, But Useful: Episode 35

In this month's Wrong, But Useful, Dave and Colin discuss: Colin gets his plug for Cracking Mathematics in early Colin is upset by a missing apostrophe Dave teases us with the number of the podcast and asks about the kinds of things it's reasonable to expect students to know, and

## A lovely trigonometric identity

When I was researching the recent Mathematical Ninja piece for Relatively Prime, I stumbled on something at MathWorld1 I'd never noticed before: if $t = \tan(x)$, then: $\tan(2x) = \frac{2t}{1 - t^2}$ $\tan(3x) = \frac{3t - t^3}{1 - 3t^2}$ $\tan(4x) = \frac{4t - 4t^3}{1 - 6t^2 + t^4}$ \$\tan(5x) =

## Ask Uncle Colin: Don’t be daunted by D’Hondt?

Dear Uncle Colin, Up here in Scotland, we've got an election tomorrow. It's not as simple as the stupid first past the post elections you have down there in England, but even with our superior Scottish intelligence, some people are still struggling to understand how the system works. Do you