题目

Both of my parents worked full-time when I was a little girl, so my grandmother would stay at our house during the day. We would watch game shows in the living room. Our favorite was The Price is Right. We would call out our answers along with the contestants. When I got older and started going to school, we couldn't watch our game shows regularly. That was okay with me, though, because the one thing I liked better than watching game shows with my grandmother was helping her bake cakes. Watching her in the kitchen was amazing: she never seemed to need the recipes but everything she made10．如图1，在平面直角坐标系中，A是第四象限内一点，AB⊥y轴于B，且C（3，0）是x轴正半轴上一点，OB-OC=2，S四边形ABOC=20．（1）求A的坐标；（2）设D是线段OB上一动点，当∠CDO=∠A时，CD与AC之间存在怎样的位置关系，写出你的结论并证明；（3）当D在线段OB上运动时，连接AD、CD，如图2，∠OCD＞∠BAD，DE平分∠ADC，DP∥AB，$\frac{∠OCD-∠BAD}{∠PDE}$是否为定值？不是，请说明理由；是，请证明之．