Question

方程组 kx - y - 4 = 0 4x^2 + 9y^2 + 18y -18 = 0中,k为何值时此方程组只有一个实

Answer 1

y+1=kx-3代入4x^2+9(y+1)^2=27.得4x^2+9(kx-3)^2=27.(9k^2+4)x^2-54kx+54=0.令其判别式=0.得54^2=4(9k^2+4)*54.解得k=正负根号(19/18)