Question

how can u tell if a question is non linear or not

Answer 1

So, a linear function doesn't have powers of a variable higher than 1

If you have an x^2, or something like that, it isn't linear.
.

Answer 2

Thanks

Answer 3

If you are looking for the linear map definition, you need to check two things.

f(x+y) = f(x) + f(y)
and
f(ax) = a f(x)

if these are true, it's a linear map (which means it basically boils down to exactly the same thing as before).

Answer 4

One last note, if you are dealing with Differential equations, the same holds true, but you can have derivatives of any order, as long as the actual power of the variable doesn't exceed 1