Choose the stems that would be used to create a stem-and-leaf plot from this data: 28, 32, 38, 30, 31, 13, 36 35, 38, 32, 38, 15, 13, 24

In a quadratic function of the form ax^2+bx+c, which of the following is not true? a. the y-intercept is c. b. if a is positive, the parabola opens up. c. the vertex has an x-coordinate of -b/2a. d. the axis of symmetry is the line y=-b/2a.