(1)把直线y=x+1代入双曲线x^2-y^2=1
即:x^2-(x+1)^2=1
x^2-x^2-2x-1=1
不是二次函数,即无焦点
(2)把直线y=kx+1代入双曲线x^2-y^2=1
即:x^2-(kx+1)^2=1
x^2-k^2x^2-2kx-1=1
(1-k^2)x^2-2kx-2=0
①1-k^2≠0
△=(2k)^2-4(1-k^2)*(-2)>0
-√2
(1)把直线y=x+1代入双曲线x^2-y^2=1
即:x^2-(x+1)^2=1
x^2-x^2-2x-1=1
不是二次函数,即无焦点
(2)把直线y=kx+1代入双曲线x^2-y^2=1
即:x^2-(kx+1)^2=1
x^2-k^2x^2-2kx-1=1
(1-k^2)x^2-2kx-2=0
①1-k^2≠0
△=(2k)^2-4(1-k^2)*(-2)>0
-√2