Answer :

crisforp
10x² + 20y² =200 / ÷ 200 ;
x^2 / 20 + y^2 / 10 = 1 ;
x^2 / [tex] ( \sqrt{20} )^{2} [/tex] + y^2 / [tex] ( \sqrt{10} )^{2} [/tex] = 1 ; 
b = [tex] \sqrt{20} [/tex] ; a = [tex] \sqrt{10} [/tex] ;
Major axis is 2a = 2[tex] \sqrt{10} [/tex] ;