2. a style of dance music marked by some of the features of jazz.
The graph of y = 2x+1 is a straight line. 1  When x increases, y increases twice as fast, hence 2x. 2  When x is 0, y is already 1.  So: y = 2x + 1.
In particular, a differential equation is linear if it is linear in terms of the unknown function and its derivatives, even if nonlinear in terms of the other variables appearing in it. As nonlinear equations are difficult to solve, nonlinear systems are commonly approximated by linear equations (linearization).