Trigonometric functions are also not linear. ... The mistake is to assume that the function f(x) = cos(x) is linear, that is that f(x+y) = f(x) + f(y). A simple counterexample shows that this function f is not linear.

Is sin a linear?

Depending upon the details of whatever situation is being addressed, it would generally be acceptable to treat the sine function as being linear over a span of 0.0001 of a single period of the sine function.

Is sin a linear equation?

Recall that ax + by = c is a linear equation in the two variables x and y. If we replace x and y with sin x and cos x then we obtain a linear equation in sin x and cos x. In other words, the equation a sin x + b cos x = c is a linear equation in sin x and cos x.