The standard equation for an ellipse with centre at the origin is:
x^2/a^2+y^2/b^2=1, where a and b are usually the semi-major and semi-minor axes.
When x=0, y=±b. 2b=14, so 2b in this case is the major axis and b=7.
When y=0, x=±a. 2a=10, and 2a is the minor axis and a=5.
x^2/25+y^2/49=1.