1, trigonometric functions include sine, cosine, tangent and cotangent, which can be remembered by a formula: an unwise cook taught his apprentice to kill fish and said this sentence: cut the fish directly. Positive: sine or tangent, right: opposite positive; Remainder: cosine or cosine, adjacent: adjacent edges indicate that the remainder is adjacent; Tangents are right-angled edges.

2. Increase or decrease of trigonometric function: positive increase and residual decrease. Memory of special trigonometric function values: firstly, remember that the denominators of sine and cosine values of 30 degrees, 45 degrees and 60 degrees are all 2, and the denominators of tangent and cotangent are all 3. Molecules can remember the formula "123,3213927".

trigonometric function

One of the basic elementary functions is a function with angle as the independent variable and the coordinates of the intersection point between the terminal edge of any angle and the unit circle or its ratio as the dependent variable. The trigonometric function relates the internal angle of a right triangle to the ratio of its two sides, and can also be defined by the lengths of various line segments related to the unit circle equivalently. Trigonometric function plays an important role in studying the properties of geometric shapes such as triangles and circles, and is also a basic mathematical tool for studying periodic phenomena.

The early study of trigonometric functions can be traced back to ancient times. The founder of trigonometry in ancient Greece was Hippocius in the 2nd century BC. He divided the circumference into 360 equal parts according to the practice of the ancient Babylonians. For a given radian, he gives the corresponding chord length, which is equivalent to the modern sine function.

Hipachas actually given the earliest numerical table of trigonometric functions. However, trigonometry in ancient Greece was basically spherical. This is related to the fact that the main body of ancient Greek research is astronomy. Menelaus described Menelaus theorem of spherical surface with sine in his book "The Science of Sphere".

The application of trigonometry and astronomy in ancient Greece reached its peak in Ptolemy's time in Egypt. Ptolemy calculated the sine values of 36-degree angle and 72-degree angle in mathematical compilation, and also gave the calculation methods of sum angle formula and half angle formula. Ptolemy also gave sine values corresponding to all integer radians and semi-integer radians from 0 to 180 degrees.