Which function represents a reflection of f (x) = 3/8 (4) x across the y-axis?

You can think of reflections as rotations of 180 degrees about the specified axis. Thus reflecting any function y = f (x), not just an exponential: About the y-axis, keeps y the same but flips the sign of x to - x. so y = f (-x) is the reflected function. About the x-axis, keeps x the same but flips the sign of y to - y so - y = f (x) or y = - f (x). So in your example of reflecting f (x) = 4x about the y-axis:y = 4 (-x) = - 4x