The coefficient of the leading term in a parabola, tells you if the parabola opens Upward or Downward, and if the parabola is horizontally Compressed, Stretched or neither.
Parabola: ax2 + bx + c
a > 0 opens Upward
a < 0 opens Downward
| a | > 1 Compresses
| a | < 1 Stretches
| a | = 1 it doesn't change
In this case:
4x2 + 9
(2x)2 + 9
The leading coefficient tell us:
a = 2
2 > 1 The parabola opens Upward
| 2 | >1 The parabola Horizontally Compresses by a factor of 2