heyy, (Barron SAT Math II Page 19)

what is the length of the major axis of the ellipse whose equation is 10x^2+20y^2=200?

a) 3.16

b)4.47

c) 6.32

d) 8.94

e) 14.14

The correct answer is D). The answer book said to divide both sides of the equation by 200 to write the equation in standard form. So then the length of the major axis is 2 . Can please explain why? What does it mean by 'major' axis ?

Thanks in advance!