Consider we need to find the equation of ellipse.
Given:
Ellipse is centered at the origin.
Major axis is horizontal, with length 8.
The length of its minor axis is 4.
To find:
The equation of ellipse.
Solution:
Major axis is horizontal, so standard form of ellipse is
[tex]\dfrac{(x-h)^2}{a^2}+\dfrac{(y-k)^2}{b^2}=1[/tex] ...(i)
where, (h,k) is center of the ellipse and length of major axis is 2a and length of minor axis is 2b.
Ellipse is centered at the origin. So, h=0 and k=0.
Major axis is horizontal, with length 8.
[tex]2a=8[/tex]
[tex]a=4[/tex]
The length of its minor axis is 4.
[tex]2b=4[/tex]
[tex]b=2[/tex]
Substitute h=0, k=0, a=4 and b=2 in equation (i).
[tex]\dfrac{(x-0)^2}{4^2}+\dfrac{(y-0)^2}{2^2}=1[/tex]
[tex]\dfrac{x^2}{16}+\dfrac{y^2}{4}=1[/tex]
Therefore, the required equation of ellipse is [tex]\dfrac{x^2}{16}+\dfrac{y^2}{4}=1[/tex].