1、c/a=√3/2,得c=√3/2a,b^2=a^2-c^2=1/4a^2,
再把(2,0)代入椭圆C的方程,易求得a^2=4,b^2=1
所以方程为:X^2/4+Y^2 =1
2,证明:设P(X.,Y.),K(A1P)=Y./(X.+2),
所以A1P的方程为:Y=Y./(X.+2)*(X+2)
当X=2√2,Y=Y./(X.+2)*(2√2+2),即│DE│=Y./(X.+2)*(2√2+2),
同理A2P的方程为:Y=Y./(X.-2)*(2√2-2),│DF│=Y./(2-X.)*(2√2-2)(因为X.小于2),
所以│DE│*│DF│=4Y.^2/(4-X.^2),又P(X.,Y.)点在椭圆X^2/4+Y^2 =1上,
所以X.^2+4Y.^2=4,即4Y.^2=4-X.^2,所以│DE│*│DF│=1