解:设点斜式方程y-1=k(x-2)(k为斜率),即kx-y-2k+1=0 联立得kx-x^2-2k+1=0 x^2-kx+2k-1=0 Δ=k^2-4(2k-1)=k^2-8k+4=0 解得k=4±2√3 直线方程为y-1=(4±2√3)(x-2)