Question

已知圆C的方程为f(x,y)=0,点A(x1,y1)在圆的内部,点B(x2,y2)在圆上,则3f（x,y）+f(x1,y

Answer 1

设f(x,y)=(x-a)^2+(y-b)^2-r^2

f(x,y)=0即(x-a)^2+(y-b)^2-r^2=0

点A(x1,y1)在圆的内部,即(x1-a)^2+(y1-b)^2