Question #202800

Let S ≡ 4x2 −9y2 −36 = 0 and S' ≡ y2 −4x = 0 be two conics. Under what conditions on k, will the conic S+kS' = 0 represent:

i) an ellipse?

ii) a hyperbola?


1
Expert's answer
2021-06-10T07:07:41-0400

The conic Ax2+Bxy+Cy2+Dx+Ey+F=0is an ellipse if B2<4ACanda hyperbola ifB24AC>0According to questionS+kS=4x2+0xy+(k9)y24kx+0y36=0is an ellipse if02<4(4)(k9)0<16k144144<16kk>9 ......conditions on k,for an ellipseNowan a hyperbola if024(4)(k9)>0016k+144>016k>144k<9 ......conditions on k,for an hyperbolaThe \space conic \space \\Ax2+Bxy+Cy2+Dx+Ey+F=0 \\ is \space an \space ellipse \space if \space \\ B^2<4AC \\and \\ a \space hyperbola \space if \\ B^2-4AC>0 \\ According \space to \space question \\ S+kS'=4x^2+0xy+(k-9)y^2-4kx+0y-36=0 \\ is \space an \space ellipse \space if \\ 0^2<4(4)(k-9) \\ 0<16k-144 \\ 144<16k \\ k>9 \\\space ......conditions \space on \space k, for \space an \space ellipse\\ Now \\ an \space a \space hyperbola \space if \\ 0^2-4(4)(k-9)>0 \\ 0-16k+144>0 \\ -16k>-144 \\ k<9 \\\space ......conditions \space on \space k, for \space an \space hyperbola\\


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