Question

k为何值时.方程x^2+y^2-2x+4y=-k^2-k+1表示一个圆______过程要详细.

Answer 1

x^2+y^2-2x+4y=-k^2-k+1

x^2-2x+1 + y^2+4y+4=-k^2-k+1+1+4=-k^2-k+6

(x-1)^2+(y+2)^2=-k^2-k+6

则 -k^2-k+6>0

k^2+k-6>0

(k+3)(k-2)>0

k>2 或 k