What effect does the "a" value have on the function f (x) = log (x)

I would guess they're referring to some general form first f (x) = alog (x-h) + k Where 'h' represents horizontal shifts, 'k' vertical shifts and 'a' stretches the function. "a" will also reflect the function across the x-axis if the value is negative. But NOT across the y-axis. I hope that's the place they wanted to put the a at least