量出下面每个三角形三个角的度数，并计算三个角的和．你有什么发现？
计算下面各题．= = = ﹣= 1﹣=﹣= = ﹣= =
看谁算得又对又快．= = == = =．
3与4的倒数之差是多少？
算一算．+= ﹣= +=+= ﹣= ﹣=
+= 1﹣= += +=1﹣= += ﹣= ﹣=
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= 1﹣
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