已知：一个圆锥的侧面展开图是半径为 20cm，圆心角为120°的扇形，求这圆锥的底半径和高．
直接计算×4=÷4= 8÷= 8×=÷= 39÷=
直接写得数．×0=×=×12=×=÷=÷= 9×=×= 18×=÷=÷=÷12=
计算×÷÷．
直接写出得数．÷5=÷4=÷2=÷3=÷=÷=÷=÷= 1÷= 15÷=÷=÷=×=×=+= 1﹣=
先看清左右两题之间的关系，再写出得数．
×4=
÷4= 8÷
= 8×
= 39÷
×0=
×
=
×12=
×
=
÷
=
÷
= 9×
=
×
= 18×
=
÷
=
÷
=
÷12=
×
÷
÷
．
÷5=
÷4=
÷2=
÷3=
÷
=
÷
=
÷
÷
=
= 15÷
=
÷
=
÷
=
×
×
=
+
= 1﹣
=
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