过点A分别画两条直线的垂线；过点B分别画两条射线的平行线．
用你喜欢的方法计算．+﹣+﹣ 5﹣﹣．
怎样简便怎样算．++=+++=﹣（+）=
．
﹣=+=+=﹣=﹣=﹣=+=﹣= 1﹣﹣=+=
+=﹣= 7.2÷0.3=﹣1=+0.2= 0.54÷9=﹣=﹣=﹣=+= 1÷0.25=+= 0.67+0.3= 0.38×2= 8.1÷0.09= 2﹣= 12×0.5= 2.5×0.6=
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= 7.2÷0.3=
﹣1=
+0.2= 0.54÷9=
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﹣
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= 1÷0.25=
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= 12×0.5= 2.5×0.6=
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