over the [tex]x[/tex]-axis, it could mean two things. it could mean on the [tex]x[/tex]-axis or it could mean above the [tex]x[/tex]-axis
if it means on the [tex]x[/tex]
-axisthen [tex]B[/tex] and [tex]D[/tex] are correct
if it means above the [tex]x[/tex]
-axis[tex]B[/tex] is correct
the value of [tex]c[/tex] is the value of [tex]y[/tex] when [tex]x = 0[/tex] (the point when the function crosses the y-axis)
since [tex]a > 0[/tex] and the function above x-axis, it must cross the positive y-axis (c is positive)
---------
when [tex]a > 0[/tex] and the turning point on the [tex]x[/tex] axis or above it
[tex]c[/tex] is positive
when [tex]a > 0[/tex] and the turning point below the [tex]x[/tex] axis
[tex]c[/tex] could be positive or negative
when [tex]a < 0[/tex] and the turning point on the [tex]x[/tex] axis or below it
[tex]c[/tex] is negative
when [tex]a < 0[/tex] and the turning point obove the [tex]x[/tex] axis
[tex]c[/tex] could be positive or negative
-Jambo