设椭圆的标准方程为:x^2/a^2 + y^2/b^2 = 1
因为:长轴上短轴的三倍,故有:a = 3b (1)
又因为:椭圆过点(3,0)
则有:3^2/a^2 + 0^2/b^2 = 1
即有:3^2/a^2 = 1,解得 a = 3或a = -3(舍去)
把a = 3代入(1)得:b = 1
所以,椭圆的标准方程是 x^2/9 + y^2 = 1
设椭圆的标准方程为:x^2/a^2 + y^2/b^2 = 1
因为:长轴上短轴的三倍,故有:a = 3b (1)
又因为:椭圆过点(3,0)
则有:3^2/a^2 + 0^2/b^2 = 1
即有:3^2/a^2 = 1,解得 a = 3或a = -3(舍去)
把a = 3代入(1)得:b = 1
所以,椭圆的标准方程是 x^2/9 + y^2 = 1