Question

已知數(shù)軸上點(diǎn)A對(duì)應(yīng)的數(shù)是-3.5．
（1）如果點(diǎn)B與點(diǎn)A相距5個(gè)單位長(zhǎng)度，那么點(diǎn)B所對(duì)應(yīng)的數(shù)是什么？
（2）如果點(diǎn)C所對(duì)應(yīng)的數(shù)是-2.5，那么（1）中的點(diǎn)B與點(diǎn)C相距多遠(yuǎn)？

Answer 1

解：（1）已知數(shù)軸上點(diǎn)A對(duì)應(yīng)的數(shù)是-3.5．B與點(diǎn)A相距5個(gè)單位長(zhǎng)度，如果B點(diǎn)在A點(diǎn)的左邊，則B點(diǎn)所對(duì)應(yīng)的數(shù)為-8.5；如果B點(diǎn)在A的右邊，則B點(diǎn)所對(duì)應(yīng)的數(shù)是1.5．
（2）如果點(diǎn)C所對(duì)應(yīng)的數(shù)是-2.5，那么（1）中的B點(diǎn)所對(duì)應(yīng)的數(shù)是-8.5時(shí)，點(diǎn)B與點(diǎn)C相距6個(gè)單位長(zhǎng)度．當(dāng)B點(diǎn)所對(duì)應(yīng)的數(shù)為1.5時(shí)．則點(diǎn)B與點(diǎn)C相距4個(gè)單位長(zhǎng)度．
分析：（1）根據(jù)數(shù)軸的定義、意義和三要素可以得知：點(diǎn)B與點(diǎn)A相距5個(gè)單位長(zhǎng)度，只有兩種結(jié)果．一是點(diǎn)B在點(diǎn)A左邊5個(gè)單位長(zhǎng)度，則點(diǎn)B所對(duì)應(yīng)的數(shù)是-8.5；二是點(diǎn)B在點(diǎn)A右邊5個(gè)單位長(zhǎng)度，則點(diǎn)B所對(duì)應(yīng)的數(shù)是1.5．所以點(diǎn)B所對(duì)應(yīng)的數(shù)是1.5或-8.5．
（2）從數(shù)軸上可以看出，點(diǎn)C與原點(diǎn)左邊的點(diǎn)B相距4個(gè)單位長(zhǎng)度，與原點(diǎn)右邊的點(diǎn)B相距6個(gè)單位長(zhǎng)度．
點(diǎn)評(píng)：此題考查了數(shù)軸的定義、意義和三要素及其應(yīng)用．