已知如图，∠AOB是锐角，以O为端点向∠AOB内部作一条射线，则图中有多少个角？若作二条、三条射线有多少个角？n条时有多少个角？画一画，你发现什么规律？
直接写出得数+=﹣=+= 1﹣=+==+=﹣= 3﹣=+= 3÷7= 43=
直接写得数．+= 3﹣1.75=÷=×=×=÷=÷=×0+3=（+）×=
直接写出得数．+=﹣=×2=×=÷3×÷3== 12×=×14=÷4=+÷+=
直接写得数+= 3+1.75=÷=×=×=﹣=+=×0+3= （+）×=×÷×=
口算下面各题．﹣=+=﹣= 2÷=×6=÷=×6=×=﹣=÷=÷=×=×=÷=÷= 6.4÷0.08= 4﹣2.92=÷=
+
=
﹣
=
+
= 1﹣
=
=
=
+
=
﹣
= 3﹣
=
+
= 3÷7= 43=
+
= 3
﹣1.75=
÷
=
×
×
=
÷
=
÷
=
×0+3=（
+
）×
=
+
=
﹣
=
×2=
×
=
÷3×
= 12×
=
×14=
÷4=
+
+
+
= 3
+1.75=
÷
=
×
=
×
=
﹣
=
+
=
×0+3=
+
）×
=
×
÷
×
﹣
=
+
=
﹣
= 2÷
=
×6=
÷
=
×6=
×
=
﹣
÷
=
÷
=
×
=
×
=
÷
=
÷
= 6.4÷0.08= 4﹣2.92=
÷
=
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