To find the equation for the reflection of a function f(x) across the y-axis, you can replace x with -x in the original function. So, if your original function is f(x) = 2x^2 + 3x - 1, the equation for g(x), the reflection of f(x) across the y-axis, would be:
g(x) = 2(-x)^2 + 3(-x) - 1
Simplify this equation to get the reflection of f(x) across the y-axis.