试题与答案

在四边形ABCD中，∠D=60°，∠B比∠A大20°，∠C是∠A的2倍，求∠A，

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题型：解答题

题目：

在四边形ABCD中，∠D=60°，∠B比∠A大20°，∠C是∠A的2倍，求∠A，∠B，∠C的大小．

答案：

设∠A=x，则∠B=x+20°，∠C=2x．

四边形内角和定理得x+（x+20°）+2x+60°=360°，

解得x=70°．

∴∠A=70°，∠B=90°，∠C=140°．

考点：多边形的内角和和外角和
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