The center of an ellipse is (-9,3). one focus is (-7,3). The major axis is 24 units long. What is the equation of the ellipse in standard form?

I got as far as ((x+9)^2)/24 + ((y-3)^2)/b^2 =1

But I don't know how to get b^2 (length of the minor axis)​

Respuesta :

Answer:

[tex]\frac{(x+9)^2}{144}+\frac{(y-3)^2}{140}=1[/tex]

Step-by-step explanation:

The standard equation of the ellipse is

[tex]\frac{(x-\alpha)^2}{a^2}+\frac{(y-\beta)^2}{b^2}=1\;\cdots(i)[/tex]

where, [tex](\alpha, \beta)[/tex] is the center and a,b are semi axes of the ellipse along x-axis and y-axis respectively.

Given that, [tex](\alpha, \beta)=(-9,3)[/tex] and major axis, [tex]2a=24[/tex].

So, semi major axis, [tex]a=24/2=12[/tex].

Now, focus of the ellipse is (-7,3).

Let [tex]e[/tex] be the eccentricity of the ellipse,

So, [tex]e=\frac c a[/tex]

where [tex]c[/tex] is the distance between the center and focus of the ellipse.

By using the distance formula,

[tex]c=\sqrt{(-9-(-7))^2+(3-3)^2}=2[/tex]

[tex]\Rightarrow e=\frac {2}{12}=\frac{1}{6}\;\cdots(ii)[/tex]

Again, the relationship among [tex]a,b[/tex] and [tex]e[/tex] is

[tex]e=\sqrt{1-\frac{b^2}{a^2}[/tex]

[tex]\Rightarrow \frac{1}{6}=\sqrt{1-\frac{b^2}{(12)^2}[/tex] [from equation (ii)]

[tex]\Rightarrow \frac{1}{36}=\sqrt{1-\frac{b^2}{144}[/tex] [squaring on both the sides]

[tex]\Rightarrow \frac{b^2}{144}=1-\frac{1}{36}[/tex]

[tex]\Rightarrow b^2=\frac{35}{36}\times144=140[/tex]

So, the value of square of semi-minir axis, [tex]b^2=140[/tex].

Hence, from equation (i), the equation of required ellipse is standard form is

[tex]\frac{(x-(-9))^2}{144}+\frac{(y-3)^2}{140}=1[/tex]

[tex]\Rightarrow \frac{(x+9)^2}{144}+\frac{(y-3)^2}{140}=1[/tex]

The equation of the ellipse is [tex]\frac{(x+9)^{2}}{144}+\frac{(y-3)^{2}}{140} = 1[/tex].

The equation of the ellipse in standard form is described below:

[tex]\frac{(x-h)^{2}}{a^{2}} + \frac{(y-k)^{2}}{b^{2}} = 1[/tex] (1)

Where:

  • [tex]h, k[/tex] - Coordinates of the center.
  • [tex]a[/tex] - Major semiaxis length.
  • [tex]b[/tex] - Minor semiaxis length.

The length of the minor semiaxis ([tex]b[/tex]) is found by using the following Pythagorean-like relationship:

[tex]b = \sqrt{a^{2}-c^{2}}[/tex] (2)

If we know that [tex](h,k) = (-9,3)[/tex], [tex]a = 12[/tex] and [tex]F_{1}(x,y) = (-7,3)[/tex], then the equation of the ellipse is:

[tex]c = \sqrt{[(-9)-(-7)]^{2}+(3-3)^{2}}[/tex]

[tex]c = 2[/tex]

[tex]b = \sqrt{12^{2}-2^{2}}[/tex]

[tex]b = 2\sqrt{35}[/tex]

Hence, the equation of the ellipse is [tex]\frac{(x+9)^{2}}{144}+\frac{(y-3)^{2}}{140} = 1[/tex].

We kindly invite to check this question on ellipses: https://brainly.com/question/14281133