The Power of Trigonometry

I was talking to some school kids a couple of years ago and they hadn't done so well in their mathematics exams age 15. How do we know the world is round? We could send a pro up into space but take a photo. The answer is there was a place where at midday at noon on the summer solstice nothing cast a shadow. By looking at the length of the shadow it's a really really simple calculation that gives you an estimate with this conference of the earth. It's only two or three percent outYou can do that with just one little tiny fact about triangles. I don't think I did. Show people the wonder and the joy and the power of mathematics.