A parabola with equationy=ax^2 is graphed in the standard coordinate plane. Suppose that the parabola is rotated clockwise by 90 degrees about the origin. Which of the following is an equation for the parabola that results from this rotation?

A. x = -ay^2

B. x = ay^2

C. y = -ax^2

The answer should be B but why can't it be A?

I thought that 90 deg. clockwise rotation about the origin was of form: (x,y)-->(y, -x) but by substitution I obtain choice A not B...