几何题的证明方法很多 ,利用代数方法来证明几何题有时显得更为直接 ,教学效果也较为显著 .1　利用方程或方程组证明几何题图 1例 1　已知 :D是△ ABC的边 AC上的一点 ,AD∶DC=2∶ 1,∠C=45°,∠ ADB=6 0°,求证 :AB是△BCD的外接圆的切线 .分析　要证 AB是△BCD的外接圆的切线 There are many ways to prove a geometric problem. The use of algebraic methods to prove geometric problems sometimes seems more direct and the teaching effects are more significant. 1 Use the equations or equations to prove a geometric problem. Figure 1 Example 1 Known: D is △ ABC on the side AC One point, AD:DC=2:1, ∠C=45°, ∠ ADB=6 0°, verify that AB is the tangent of the circumscribed circle of ΔBCD. The analysis proves that AB is the tangent of the circumscribed circle of ΔBCD.