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人教版六年級數(shù)學(xué)上冊第四單元,課題：確定起跑線 教學(xué)時間：一課時 單位：木壘縣雀仁鄉(xiāng)中心學(xué)校 姓名：蔡淑英,1,確定起跑線,2,,,,,,,,,,,,,,,,,,,,,1,,3,,2,,終點線,3,4,5,,,,,,,,,,,,,,,,,,,,,,,,,,85.96m,,,72.6m,,1.25m,,1.25m,,1.25m,6,7,,,,,,,,,,,,,,,,,,,,,,,,,,,85.96m,,,72.6m,,,1.25m,1.25m,1.25m,,,,8,9,注：π取3.14159,10,,,,,,,,,,,,,,,,,,,,,,,,,85.96m,,,72.6m,,,,,第一道,直徑：,周長：,全長：,72.6m,72.63.14159≈228.08（m）,85.962＋228.08=400（m）,11,72.6,228.08,400,注：π取3.14159,12,,,,,,,,,,,,,,,,,,,,,,,,,85.96m,,,72.6m,,,,,第一道,直徑：,周長：,全長：,72.6m,228.08m,400m,第二道,直徑：,周長：,全長：,72.6＋1.25＋1.25=75.1（m）,75.13.14159≈235.93（m）,85.962＋235.93=407.85（m）,,,1.25m,1.25m,13,72.6,228.08,400,75.1,235.93,407.85,注：π取3.14159,14,,,,,,,,,,,,,,,,,,,,,,,,,85.96m,,,72.6m,,,,,第二道,直徑：,周長：,全長：,75.1m,235.93m,407.85m,第三道,直徑：,周長：,全長：,75.1＋1.25＋1.25=77.6（m）,77.63.14159≈243.79（m）,85.962＋243.79=415.71（m）,,,1.25m,1.25m,,75.1m,15,72.6,228.08,400,75.1,235.93,407.85,77.6,243.79,415.71,注：π取3.14159,16,,,,,,,,,,,,,,,,,,,,,,,,,85.96m,,,72.6m,,,,,第三道,直徑：,周長：,全長：,77.6m,243.79m,415.71m,第四道,直徑：,周長：,全長：,77.6＋1.25＋1.25=80.1（m）,80.13.14159≈251.64（m）,85.962＋251.64=423.56（m）,,,1.25m,1.25m,,77.6m,17,72.6,228.08,400,75.1,235.93,407.85,77.6,243.79,415.71,80.1,251.64,423.56,注：π取3.14159,18,,,,,,,,,,,,,,,,,,,,,,,,,85.96m,,,72.6m,第四道,直徑：,周長：,全長：,80.1m,251.64m,423.56m,第五道,直徑：,周長：,全長：,80.1＋1.25＋1.25=82.6（m）,82.63.14159≈259.50（m）,85.962＋259.5=431.42（m）,19,72.6,228.08,400,75.1,235.93,407.85,77.6,243.79,415.71,80.1,251.64,423.56,82.6,259.5,431.42,注：π取3.14159,20,,,,,,,,,,,,,,,,,,,,,,,,,85.96m,,,72.6m,第五道,直徑：,周長：,全長：,82.6m,259.5m,431.42m,第六道,直徑：,周長：,全長：,82.6＋1.25＋1.25=85.1（m）,85.13.14159≈267.35（m）,85.962＋267.35=439.27（m）,21,72.6,228.08,400,75.1,235.93,407.85,77.6,243.79,415.71,80.1,251.64,423.56,82.6,259.5,431.42,85.1,267.35,439.27,注：π取3.14159,22,,,,,,,,,,,,,,,,,,,,,,,,,85.96m,,,72.6m,第六道,直徑：,周長：,全長：,85.1m,267.35m,439.27m,第七道,直徑：,周長：,全長：,85.1＋1.25＋1.25=87.6（m）,87.63.14159≈275.20（m）,85.962＋275.2=447.12（m）,23,72.6,228.08,400,75.1,235.93,407.85,77.6,243.79,415.71,80.1,251.64,423.56,82.6,259.5,431.42,85.1,267.35,439.27,87.6,275.2,447.12,注：π取3.14159,24,,,,,,,,,,,,,,,,,,,,,,,,,85.96m,,,72.6m,第七道,直徑：,周長：,全長：,87.6m,275.2m,447.12m,第八道,直徑：,周長：,全長：,87.6＋1.25＋1.25=90.1（m）,90.13.14159≈283.06（m）,85.962＋283.06=454.98（m）,25,72.6,228.08,400,75.1,235.93,407.85,77.6,243.79,415.71,80.1,251.64,423.56,82.6,259.5,431.42,85.1,267.35,439.27,87.6,275.2,447.12,90.1,283.06,454.98,注：π取3.14159,各跑道的起跑線應(yīng)該相差多少米？,7.85m,/ 7.86m,7.85,,7.86,,7.85,,7.86,,7.85,,7.85,,7.86,,26,,72.6,228.08,400,75.1,235.93,407.85,77.6,243.79,415.71,80.1,251.64,423.56,82.6,259.5,431.42,85.1,267.35,439.27,87.6,275.2,447.12,90.1,283.06,454.98,注：π取3.14159,27,我不用算出每條跑道的長度，也知道它們相差多少米?,兩條直道是一樣的，所以只需要看圓的周長。圓的周長是這樣算的：,第一道：72.6π,第二道：(72.6＋2.5)π = 72.6π＋2.5π,第三道：(75.1＋2.5)π = 75.1π＋2.5π,第四道：(77.6＋2.5)π = 77.6π＋2.5π,第五道：(80.1＋2.5)π = 80.1π＋2.5π,第六道：(82.6＋2.5)π = 82.6π＋2.5π,第七道：(85.1＋2.5)π = 85.1π＋2.5π,第八道：(87.6＋2.5)π = 87.6π＋2.5π,每一條跑道都在上一條跑道的基礎(chǔ)上增加2.5π的長度。你能算出2.5π是多少米嗎？,28,,,,,,,,,,,,,,,,,,,,,終點,起點,200米的跑道，每條道的長度都是它們?nèi)L的一半。,第一條：4002=200（m）,第二條：407.852=203.925（m）,第三條：415.712=207.855（m）,第四條：423.562=211.78（m）,第五條：431.422=215.71（m）,每條道相差3.925m或3,39m。所以起跑線應(yīng)依次提前約3.925m。,思考：200米跑步比賽，跑道寬為1.25米，起跑線應(yīng)依次提前多少米？,29,本節(jié)課你有收獲嗎？ 說說與大家分享一下吧！,30,