Basic TrigonometryThere are six basic trigonometric functions. Consider a rightangled triangle, one of whose other angles is x as in the figure below:The basic functions are defined in terms of the length of the Hypotenuse (the longest side), the side Opposite the angle x, and the side Adjacent to angle x. The sine of x, written as sin(x) is defined as:
The cosine of x, written as cos(x) is defined as:
The tangent of x, written as tan(x) is defined as:
Note that tan(x) is undefined where x = 0. Using these functions, if an angle and the length of one side of a rightangled triangle are known, the length of the other two sides can easily be calculated.
The other three functions are the secant, cosecant, and cotangent  these are the reciprocal of the sine, cosine and tangent respectively. This is important, because the notation sin^{1}(x) is used to indicate the inverse sine function, or arc sine  that is, the angle whose sine is x. Similar notations apply to the arc cosine and arc tangent. Quick examination of the table above shows that the arc functions can deliver multiple answers for any given value  physical examination of the problem is usually required in order to determine which range the angle falls into. Some useful functions:
By substituting x = y in the above formulae, we obtain:
