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Complete the square in the given equation to obtain the standard form and identify the conic section.
Conic section: Ellipse
Equation: (x-3)^2/36+(y+2)^2/9=1
Graph:
Let's rewrite the given equation in order to identify the conic section. We will do it by completing the square.
Rewrite - 11 as 9+16-36
Commutative Property of Addition
LHS+36=RHS+36
Factor out 4
a^2± 2ab+b^2=(a± b)^2
.LHS /36.=.RHS /36.
Write as a sum of fractions
a/b=.a /4./.b /4.
Write as a power
a+b=a-(- b)
We can see that the binomials containing the variables are both raised to the power of 2 and are both positive. Moreover, the denominator of the binomial containing the x-variable is greater than the denominator of the binomial that contains the y-variable. Therefore, our equation matches the format of a horizontal ellipse.
Let's recall the main characteristics of this type of ellipse.
| Horizontal Ellipse | |
|---|---|
| Standard-Form Equation | (x- h)^2/a^2+(y- k)^2/b^2=1 |
| Center | ( h, k) |
| Vertices | ( h± a, k) |
| Co-vertices | ( h, k± b) |
| Foci | ( h± c, k) |
| a,b,c relationship, a>b>0 | c^2= a^2- b^2 |
Consider our equation one more time. (x- 3)^2/6^2+(y-( - 2))^2/3^2=1 We see that a= 6, b= 3, h= 3, and k= - 2. The only value we do not know is c. Let's find it!
b= 3, a= 6
Calculate power
Subtract term
sqrt(LHS)=sqrt(RHS)
Split into factors
sqrt(a* b)=sqrt(a)*sqrt(b)
Note that we only took the principal root, because to find the foci we will add and subtract the value of c. Therefore, its sign is irrelevant. We can now write the desired information.
| Center | Foci |
|---|---|
| ( 3, - 2) | ( 3 ± 3sqrt(3), - 2) ⇓ ( 3+3sqrt(3), - 2 ) and ( 3-3sqrt(3),- 2 ) |
Let's find the vertices and the co-vertices.
| Vertices | Co-vertices |
|---|---|
| ( 3± 6, - 2) ⇓ (9,- 2) and (- 3,- 2) |
( 3, - 2± 3) ⇓ (3,1) and (3,- 5) |
To graph the ellipse, we plot the vertices and co-vertices. Then, we connect them with a smooth curve.