How to use trig function keys on my casio fx-300ES

Hello,
You have 3 keys for the main trigonometric functions: [SIN], [COS] and [TAN]
To use them correctly you must set the angle unit to the one your problem calls for.
Press [SIFT][MODE] [3:Deg] for degree, [4:Rad] for radian, [5:Grad] for grad. Dependig on angle unit chosen a small D, R, or G appears on the top of the screen.

If you need the inverse trigonometric functions arcsine, arccosine, arctangent, you access them by first pressing the [SHIFT] key
Thus
arcsine [SHIFT][SIN] (sin^-1)
arcosine [SHIFT][COS] (cos^-1)
arctangent [SHIFT][TAN] (tan^-1)

The syntax for the function is
[SIN] # [ ) ] [=]; [SIN] 30 [ ) ] [=] gives 0.5
[COS] # [ ) ] [=] [COS] 19 [ ) ] [=] gives 0.945518576

Note: if the argument of the functions are numbers, the right parenthesis is not necessary. But if the argument is an expression (with various operations) better put the parenthesis to make sure the calculator is performing as one wants it to.

By the way, there are no keys, or key combinations to calculate cotangent, cosecant, and secant, but you can use the definitions:

cotangent (x) = 1/tan(x) Do not confuse it with tan^-1
cosecant(x) = 1/sin(x) Do not confuse it with sin^-1
secant(x) = 1/cos(x) Do not confuse it with cos^-1

Hope it helps.