Substitution in functions is the process of replacing a variable or expression with another variable or expression.
For example, if you have a function f(x) = x^2 + 3x - 2 and you want to substitute x with 2, then you would replace x with 2 in the function to get:
f(2) = 2^2 + 3(2) - 2 = 8
This is equivalent to evaluating the function at x = 2.
In general, to substitute a variable or expression in a function, you simply replace the variable or expression with the new value or expression.
For example, if you have a function f(x) = x^2 + 3x - 2 and you want to substitute x with (y - 1), then you would replace x with (y - 1) in the function to get:
f(y - 1) = (y - 1)^2 + 3(y - 1) - 2
This is equivalent to evaluating the function at x = (y - 1).
I hope this helps!