A horizontal shrink (compression) of 2.
f(2x)2+ 3 ⇒4x2 + 3
A vertical stretch would create 4x2 + 12.
Note: vertical stretches are applied to the entire function, that is, the output of the function:
a*f(x)
If f(x) = x2+ 3, then 4*f(x) = 4(x2+3) = 4x2 + 12.
Horizontal stretches and shrinks are applied to the input of the function, inside the parentheses:
f(ax).
If there was a vertical displacement, as is true in this case, it would be outside the parentheses and would not be affected by a horizontal stretch or shrink.