Question

How do I rotate a parabola from opening up to opening horizontally?

Answer 1

instead of being f(x)={some function of x}, switch the variables to f(y)={some function of y}

Answer 2

-- take the equation of the parabola

-- wherever you see 'y' in the equation, write 'x'

-- wherever you see 'x' in the equation, write 'y'