Can you just use any shit you want for the limit? Is this true:
\[\lim_{x \to a} f(x) = \lim_{c \cdot x \to a} f(c \cdot x)?\]
The book I am reading did not properly define limits yet but used something like \(\lim_{-x \to a} f(-x)\) in one of the examples and being able to multiply the variable with any constant would be very useful for one of the exercises.