### Degree Ceremony

What does Pythagoras' Theorem tell you about these angles: 90°, (45+x)° and (45-x)° in a triangle?

### After Thought

Which is larger cos(sin x) or sin(cos x) ? Does this depend on x ?

### Small Steps

Two problems about infinite processes where smaller and smaller steps are taken and you have to discover what happens in the limit.

# Taking Trigonometry Series-ly

##### Age 16 to 18Challenge Level

We know that $\sin(x)$ and $\cos(x)$ both satisfy the equation, so try substituting $f(x) = \sin(x)$ into the differential equation.