There is a learning trick that can help you keep the functions straight. Simply remember this sentence:

Oscar Had A Heap Of Apples.

Memorizing this sentence allows you to keep the functions in correct order. As you can see, this phrase uses the first letter of each of the sides.

What you have to remember is sin, cos, tan, and Oscar had a heap of apples.

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The other functions are remembered by the order in which they are placed.

1. Sine - Cosecant: You can't have the two S's or the two Co's on the same line.

2. Cosine - Secant: You can't have the two S's or the two Co's on the same line.

3. Tangent - Cotangent: The tangent and the cotangent are easy to remember.

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The third part of remembering the
order is to realize that the functions
on the right side of the chart are
inverse to the functions on the left side.
What this means is that the numerators
and denominators are in opposite
positions.
If you need the secant to an angle, just remember that the secant is across from the cosine (therefore its inverse) and cosine relates to the second pair of words in

Oscar Had A Heap Of Apples.

This means that cosine is , so secant is .