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Mathematics 21 Online
OpenStudy (darkbluechocobo):

Help with classifying conics by discriminant

OpenStudy (darkbluechocobo):

Identify all the possible values for A in the following equation that would make the conic section a hyperbola: Ax2 − 3xy + 4y2 − 5 = 0

OpenStudy (darkbluechocobo):

So if its a hyperbola we use: B^2 − 4AC > 0

OpenStudy (darkbluechocobo):

-3^2-4(1)(4)

OpenStudy (darkbluechocobo):

9-16

OpenStudy (darkbluechocobo):

@Nnesha

OpenStudy (darkbluechocobo):

-7>0

OpenStudy (darkbluechocobo):

@perl did I do something wrong since -7 is not greater than 0?

OpenStudy (michele_laino):

In general we can write this: given the subsequent quadratic equation: \[\Large a{x^2} + bxy + c{y^2} + dx + ey + f = 0\] we have: \[\Large \begin{gathered} \Delta = {b^2} - 4ac < 0\;\left( {ellipse} \right) \hfill \\ \Delta = {b^2} - 4ac = 0\;\left( {parabola} \right) \hfill \\ \Delta = {b^2} - 4ac > 0\;\left( {hyperbola} \right) \hfill \\ \end{gathered} \]

OpenStudy (darkbluechocobo):

Indeed then I believe I set up the equation right. I am just confused on what I did because -7 is not greater than 0 s: This would be an ellipse if so

OpenStudy (michele_laino):

if A=1 (in your equation) then \Delta =-7 <0, so your conic is an ellipse

OpenStudy (perl):

ax2 − 3xy + 4y2 − 5 = 0 a= 1 b = -3 c = 4 d = 0 e = 0 f = -5 To make a hyperbola you need b^2 -4ac > 0 (-3)^2 - 4(a)(4) > 0 9 - 16a >0 9 > 16a a < 9/16

OpenStudy (darkbluechocobo):

ohhh so you ahve to keep A an exponent

OpenStudy (perl):

`a` as a constant

OpenStudy (darkbluechocobo):

No exponent i mean variable T_T

OpenStudy (michele_laino):

A is a coefficient

OpenStudy (michele_laino):

A is a factor

OpenStudy (perl):

right, think of it as a parameter ;)

OpenStudy (perl):

different specific values of `a` give you different hyperbolas. but strictly speaking x and y are the variables

OpenStudy (perl):

we are finding the set of parameters 'a' that cause the conic to be hyperbola

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