A constant is an unchangeable quantity, and a definite quantity can also be called a value. A variable, as its name implies, is a variable quantity or value.

For example, the average velocity of a simple free fall is v= 1/2gt, where g represents the acceleration of gravity, which is constant and is about 9.8m/s 2. T is a variable, a time variable. In fact, the value of t is limited, because this object will always fall to the ground anyway. The initial moment is when t equals 0.

Give a simple linear function to illustrate, such as y=2x+ 1, where slope 2 and constant 1 are constants; X is an independent variable. If x has a range of values, it can also be called a domain. For example, given that the domain of X is (representing a closed interval from 0 to 2), X can take any real number in this interval (depending on the limitation of the topic, whether it is a real number range or an integer range). Meanwhile, the value range of y is [1, 5].