which of the following functions is not linear?
a)for all x€R, f(x)=(x; 2x)
b) for all (x; y; z)€R3, f(x; y; z)=x-2y+3z
c) for all (x; y) € R2, f(x; y)= (x+1; y-1)
d) they're all linear
I hope it's clear enough to understand...These things are driving me crazy, any help is really appreciated..thanks