Answer:
Major axis (0, +-14)
Step-by-step explanation:
The equation of an ellipse with the center in the origin is:

So, to transform the equation into this form, we need to divide both sides by 784 as:

It means that a² = 16 and b² = 49. So, a = ±4 and b = ±7
Now, the major axis is 2 times the greater value between a and b. Since the greater value is b = 7, 2 times b is:
Major axis = (0, ±7*2) = (0, ±14)