# Trig function names: math history?

1. Jul 11, 2005

### EnumaElish

Does anyone know how the function names sin, cos, csc, sec, ... came about?

Wouldn't they be easier to remember if cos was 1/sin; csc was 1/sec; just like cot is 1/tan? (Instead of 1/sin = csc and 1/cos = sec.)

This is one thing in trig that always throws me off.

2. Jul 11, 2005

### TenaliRaman

3. Jul 12, 2005

### Galileo

Bah. Here we just learn sin, cos and tan. Period.
Why use extra terms (csc, sec cot) for 1/sin etc. You hardly encounter them anywhere anyway. Trig is complicated enough with all the relations among sin, cos and tan. It's only making it more complicated.

4. Jul 12, 2005

### HallsofIvy

The "co" is from the fact that the cosine is the sine of the complementary angle (90 degrees minus &theta;- the other angle in the right triangle). Same for cotangent, cosecant. Perfectly reasonable.