The conic Ax2+Bxy+Cy2+Dx+Ey+F=0is an ellipse if B2<4ACanda hyperbola ifB2−4AC>0According to questionS+kS′=4x2+0xy+(k−9)y2−4kx+0y−36=0is an ellipse if02<4(4)(k−9)0<16k−144144<16kk>9 ......conditions on k,for an ellipseNowan a hyperbola if02−4(4)(k−9)>00−16k+144>0−16k>−144k<9 ......conditions on k,for an hyperbola
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