Exercise 72 Page 885

We will find the desired information and use it to draw the graph of the hyperbola.

Vertices, Foci, and Asymptotes

Let's start by recalling the equation of hyperbolas centered at the origin. ccc Horizontal & & Vertical Hyperbola & & Hyperbola x^2/a^2-y^2/b^2=1 & & y^2/a^2-x^2/b^2=1 Now we will rewrite the given equation to match one of these formats.

x^2-36y^2=36

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Simplify

DivEqn

.LHS /36.=.RHS /36.

x^2-36y^2/36=1

WriteDiffFrac

Write as a difference of fractions

x^2/36-36y^2/36=1

ReduceFrac

a/b=.a /36./.b /36.

x^2/36-y^2/1=1

WritePow

Write as a power

x^2/6^2-y^2/1^2=1

From the above formula we can see that the equation represents a horizontal hyperbola. Next, let's review the main characteristics of this type of hyperbola.

Horizontal Hyperbola with Center (0,0)
Equation	x^2/a^2-y^2/b^2=1
Transverse axis	Horizontal
Vertices	(± a,0)
Foci	(± c,0), where c^2= a^2+ b^2
Asymptotes	y=± b/ax

Using this information, we can identify that the vertices are ( ± 6,0 ). Let's substitute a=6 and b=1 into the formula for the asymptotes and obtain their equations.

y=± b/ax

SubstituteII

a= 6, b= 1

y=± 1/6x

The asymptotes are y=± 16x. Now let's calculate c, the absolute value of the nonzero coordinate of the foci. To do so we will substitute a=6 and b=1 into c^2=a^2+b^2.

c^2=a^2+b^2

SubstituteII

a= 6, b= 1

c^2= 6^2+ 1^2

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Solve for c

CalcPow

Calculate power

c^2=36+1

AddTerms

Add terms

c^2=37

SqrtEqn

sqrt(LHS)=sqrt(RHS)

c= sqrt(37)

Note that when solving the above equation, we only needed to consider the principal root because c is a positive number. The foci of the hyperbola are (± sqrt(37),0).

Graph

To graph the function let's summarize all of the information that we have found.

Equation	x^2/6^2-y^2/1^2=1
Transverse axis	Horizontal
Vertices	(± 6,0)
Foci	(± sqrt(37),0)
Asymptotes	y=± 1/6x

Finally, we can graph our hyperbola!