|
Question 385429: this is from the shifted conics sections, you have to identify whether it is a parabola, ellipse or hyperbola, and solve and graph the problem: 2x^2 + y^2 = 2y + 1
Answer by Edwin McCravy(20059) (Show Source):
You can put this solution on YOUR website!
2x² + y² = 2y + 1
We place it in the form
Ax² + Bxy + Cy² + Dx + Ey + F = 0
2x² + 0xy + 1y² + 0x - 2y - 1 = 0
A = 2
B = 0
C = 1
D = 0
E = -2
F = -1
The rules are:
1. if the discriminant, B² − 4AC < 0, the equation represents an ellipse;
2. if A = C and B = 0, the equation represents a circle;
3. if B2 − 4AC = 0, the equation represents a parabola;
4. if B2 − 4AC > 0, the equation represents a hyperbola;
5. if we also have A + C = 0, the equation represents a rectangular hyperbola.
The discriminant is B²-4AC = 0²-4(2)(1) = -8, so it represents an ellipse.
Since it has no xy term, we get it into one of these forms
or
Either way we begin by getting the constant on the right side:
2x² + y² - 2y = 1
We complete the square on y by adding 1 to both sides:
2x² + y² - 2y + 1 = 1 + 1
We factor the last three terms on the left as a perfect square:
2x² + (y - 1)² = 2
We divide through by 2 to get 1 on the right side:
We write x as (x-0)
Write the first term over 1
That is the form
because a is always greater than b in an ellipse.
It has center (h,k) = (0,1), semi-major axis = a = 1,
and semi-minor axis = b =
It has its major axis vertical because a² is under the term in y
We plot the center:
We draw the complete major axis , about 1.4 units up and down
from the center (in purple):
We draw the complete minor axis unit right and left
from the center (in green):
We sketch in the ellipse:
Edwin
|
|
|
| |