Chapter 9.3, Problem 21E

To determine

To find: The center, vertices, foci and asymptotes of the hyperbola equation $x^2-y^2=1$ and sketch its graph using the asymptotes as an aid and use graphing utility to verify you graph.

Answer to Problem 21E

The center is $\left(0,0\right)$ , vertices is $\left(\pm 1,0\right)$ , foci is $\left(\pm \sqrt{2},0\right)$ and asymptotes is $y=\pm x$ .

Explanation of Solution

Given information:

The equation of hyperbola is $x^2-y^2=1$ .

Calculation:

Rewrite the equation in standard form as follows.

  $\frac{{\left(x-0\right)}^2}{1^2}-\frac{{\left(y-0\right)}^2}{1^2}=1$

Compare the equation $x^2-y^2=1$ with standard equation $\frac{{\left(x-h\right)}^2}{a^2}-\frac{{\left(y-k\right)}^2}{b^2}=1$ .

Therefore, the center of the hyperbola is $\left(h,k\right)=\left(0,0\right)$ and $a=1,b=1$ .

The vertices $\left(h+a,k\right)$ and $\left(h-a,k\right)$ are the two bending points of the hyperbola with the center $\left(h,k\right)$ and the semi axis $a$ and $b$ .

Find the vertices as follows.

  $\begin{array}{c}\left(h+a,k\right)=\left(0+1,0\right)\\ =\left(1,0\right)\\ \left(h-a,k\right)=\left(0-1,0\right)\\ =\left(-1,0\right)\end{array}$

For right-left facing hyperbola, the foci are defined as $\left(h+c,k\right)$ and $\left(h-c,k\right)$ , where $c=\sqrt{a^2+b^2}$ is the distance from the center $\left(h,k\right)$ to a focus.

Calculate the value of $c$ by substituting the value of $a$ and $b$ in the equation $c=\sqrt{a^2+b^2}$ .

  $\begin{array}{c}c=\sqrt{1^2+1^2}\\ =\sqrt{1+1}\\ =\sqrt{2}\end{array}$

Find the focus point as follows.

  $\begin{array}{c}\left(h+c,k\right)=\left(0+\sqrt{2},0\right)\\ =\left(\sqrt{2},0\right)\\ \left(h-c,k\right)=\left(0-\sqrt{2},0\right)\\ =\left(-\sqrt{2},0\right)\end{array}$

Substitute 1 for $a$ , $1$ for $b$ , 0 for $h$ and 0 for $k$ in the equation $y=\pm \frac{b}{a}\left(x-h\right)+k$ to find the asymptotes.

  $\begin{array}{c}y=\pm \frac{1}{1}\left(x-0\right)+0\\ =\pm x\end{array}$

Sketch the graph with the asymptotes as shown below.

  

Verify the graph by using graphing utility as shown below.

  

Therefore, the center is $\left(0,0\right)$ , vertices is $\left(\pm 1,0\right)$ , foci is $\left(\pm \sqrt{2},0\right)$ and asymptotes is $y=\pm x$ .