1)x^2+y^2=7k和2kx+y^2=3(k^2+1)】由实数解 x^2+y^2=7k>0
2kx+7k-x*x=3k*k+3即x*x-2kx+3k*k-7k+3=0有实数解判别式det>=0 0.5