设方程是x^2/a^2+y^2/b^2=1
(1)长轴是短轴的3倍,a=3b,
椭圆经过点P(3,0);b=3,a=9
方程:x^2/81+y^2/9=1
(2)离心率是0.8,焦距是8.e=c/a=0.8,c=8/2=4
a=c/e=5
b^2=a^2-c^2=25-16=9
方程:x^2/25+y^2/9=1