Applying mathematics in studying of laws of nature and using them in technique, we meet with *constants *and * variables*. A *variable*
is a value, which can be changed at the conditions of the considered problem; a *constant* cannot be changed at these conditions. The same value
can be a constant for one problem and a variable for the other.

E x a m p l e . An acceleration of a gravity is a constant for the same width of Earth, but it

changes depending on a width, i.e. in other words is a variable.

Variables are marked usually by the last letters of the Latin alphabet: *x, y, z, …* and constants – by the first ones: *a,
b, c, … .*