切线方程为Y=-1/2*X+b X=2B-2Y
切点与x^2+y^2=16(圆心为原点)相切,切点与原点（圆心）构成直线斜率K1为Y/X,与切线相垂直,K1*(-1/2)=-1 Y/X*1/2=1 Y=2X 又X=2B-2Y,代入：x^2+y^2=16
b=2根号5或=-2根号5 X=2B/5=(4/5)*根号5或-(4/5)*根号5 Y=(8/5)*根号5或-(8/5)*根号5
切线方程为Y=-1/2*X+2根号5
或切线方程为Y=-1/2*X-2根号5
切点坐标：(4/5)*根号5,(8/5)*根号5
或-(4/5)*根号5,-(8/5)*根号5