The correct pronunciation of the word sine is Zheng XIá n, initials and X, finals and Iá n, and the tones are the fourth and second tones.

Expression: Sine is a mathematical term. In a right triangle, the ratio of the opposite side to the hypotenuse of any acute angle ∠A is called the sine of ∠A, which is abbreviated from the English word sine, that is, the opposite side/hypotenuse of Sina = ∠ A.

Properties of sine function:

1, monotonic interval: sine function monotonically increases on [-π/2+2kπ, π/2+2kπ] and monotonically decreases on [π/2+2kπ, 3π/2+2kπ].

2. Parity: The sine function is odd function.

3. Symmetry: the sine function is symmetric about x=π/2+2kπ axis and symmetric about (kπ, 0) center.

4. Periodicity: The period of sine and cosine function is 2π.