Solution - Properties of ellipses

$$a$$ represents the longer radius of the ellipse, which is equal to half of the major axis.
This is called the semi-major axis.
To find the value of $$a$$, use the vertical ellipse standard form:
$$\frac{{\left(x-h\right)}^2}{b^2}+\frac{{\left(y-k\right)}^2}{a^2}=1$$

$$\frac{x^2}{49}+\frac{y^2}{81}=1$$
$$a^2=81$$
Take the square root of both sides of the equation:
$$a=9$$

Because $$a$$ represents a distance, it only has a positive value.

In a vertical ellipse, the major axis runs parallel to the y-axis and passes through the ellipse's vertices. Find the vertices by adding and subtracting $$a$$ from the y-coordinate ($$k$$) of the center.

To find vertex_1, add $$a$$ to the y-coordinate ($$k$$) of the center:
Vertex_1: $$\left(h,k+a\right)$$
Center: $$\left(h,k\right)=\left(0,0\right)$$
$$h=0$$
$$k=0$$
$$a=9$$
Vertex_1: $$\left(0,0+9\right)$$
Vertex_1: $$\left(0,9\right)$$

To find vertex_2, subtract $$a$$ from the y-coordinate ($$k$$) of the center:
Vertex_2: $$\left(h,k-a\right)$$
Center: $$\left(h,k\right)=\left(0,0\right)$$
$$h=0$$
$$k=0$$
$$a=9$$
Vertex_2: $$\left(0,0-9\right)$$
Vertex_2: $$\left(0,-9\right)$$

$$b$$ represents the shorter radius of the ellipse, which is equal to half of the minor axis. This is called the semi-minor axis.
To find the value of $$b$$, use the vertical ellipse standard form:
$$\frac{{\left(x-h\right)}^2}{b^2}+\frac{{\left(y-k\right)}^2}{a^2}=1$$

$$\frac{x^2}{49}+\frac{y^2}{81}=1$$
$$b^2=49$$
Take the square root of both sides of the equation:
$$b=7$$
Because b represents a distance, it only has a positive value.

In a vertical ellipse, the minor axis runs parallel to the x-axis and passes through the ellipse's co-vertices.
Find the co-vertices by adding and subtracting $$b$$ from the x-coordinate ($$h$$) of the center.

To find co-vertex_1, add $$b$$ to the x-coordinate ($$h$$) of the center:
Co-vertex_1: $$\left(h+b,k\right)$$
Center: $$\left(h,k\right)=\left(0,0\right)$$
$$h=0$$
$$k=0$$
$$b=7$$
Co-vertex_1: $$\left(0+7,0\right)$$
Co-vertex_1: $$\left(7,0\right)$$

To find co-vertex_2, subtract $$b$$ from the x-coordinate ($$h$$) of the center:
Co-vertex_2: $$\left(h-b,k\right)$$
Center: $$\left(h,k\right)=\left(0,0\right)$$
$$h=0$$
$$k=0$$
$$b=7$$
Co-vertex_2: $$\left(0-7,0\right)$$
Co-vertex_2: $$\left(-7,0\right)$$

Focal length is the distance from the ellipse's center to each focal point and is usually represented by $$f$$.

To find $$f$$, use the formula:
$$f=\sqrt{a^2-b^2}$$
$$a^2=81$$
$$b^2=49$$
Plug $$a^2$$ and $$b^2$$ into the formula and simplify:

$$f=\sqrt{81-49}$$

$$f=\sqrt{32}$$

$$f=5.657$$

Because $$f$$ represents a distance, it only has a positive value.

In a vertical ellipse, the major axis runs parallel to the y-axis and through the foci.
Find the foci by adding and subtracting $$f$$ from the y-coordinate $$\left(k\right)$$ of the center.

To find focus_1, add $$f$$ to the y-coordinate $$\left(k\right)$$ of the center:
Focus_1: $$\left(h,k+f\right)$$
Center: $$\left(h,k\right)=\left(0,0\right)$$
$$h=0$$
$$k=0$$
$$f=5.657$$
Focus_1: $$\left(0,0+5.657\right)$$
Focus_1: $$\left(0,5.657\right)$$

To find focus_2, subtract $$f$$ from the y-coordinate $$\left(k\right)$$ of the center:
Focus_2: $$\left(h,k-f\right)$$
Center: $$\left(h,k\right)=\left(0,0\right)$$
$$h=0$$
$$k=0$$
$$f=5.657$$
Focus_2: $$\left(0,0-5.657\right)$$
Focus_2: $$\left(0,-5.657\right)$$

Use the formula for the area of an ellipse to find the ellipse's area:
$$\pi ·a·b$$
$$a=9$$
$$b=7$$
Plug $$a$$ and $$b$$ into the formula and simplify:

$$\pi ·9·7$$

$$\pi ·63$$

The area equals $$63\pi$$

To find the x-intercept(s), plug $$0$$ in for $$y$$ in the ellipse's standard equation and solve the resulting quadratic equation for $$x$$.
Click here for a step-by-step explanation of the quadratic equation.

$$\frac{x^2}{49}+\frac{y^2}{81}=1$$

$$\frac{x^2}{49}+\frac{0^2}{81}=1$$

$$x_1=7$$

$$x_2=-7$$

To find the y-intercept(s), plug $$0$$ in for $$x$$ in the ellipse's standard equation and solve the resulting quadratic equation for $$y$$.
Click here for a step-by-step explanation of the quadratic equation.

$$\frac{x^2}{49}+\frac{y^2}{81}=1$$

$$\frac{0^2}{49}+\frac{y^2}{81}=1$$

$$y_1=9$$

$$y_2=-9$$

To find the eccentricity use the formula:
$$\frac{\sqrt{a^2-b^2}}{a}$$
$$a^2=81$$
$$b^2=49$$
$$a=9$$
Plug $$a^2$$ , $$b^2$$ and $$a$$into the formula:

$$\frac{\sqrt{81-49}}{9}$$

$$\frac{\sqrt{32}}{9}$$

$$\frac{5.657}{9}$$

$$0.629$$

The eccentricity equals $$0.629$$