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1、确定起跑线,1,3,2,终点线,情境导入,探索新知,探索新知,85.96m,72.6m,1.25m,1.25m,1.25m,探索新知,探索新知,85.96m,72.6m,1.25m,1.25m,1.25m,探索新知,探索新知,注：取3.14159,探索新知,85.96m,72.6m,第一道,直径：,周长：,全长：,72.6m,72.63.14159228.08（m）,85.962228.08=400（m）,探索新知,72.6,228.08,400,注：取3.14159,探索新知,85.96m,72.6m,第一道,直径：,周长：,全长：,72.6m,228.08m,400m,第二道,直径：,周长
2、：,全长：,72.61.251.25=75.1（m）,75.13.14159235.93（m）,85.962235.93=407.85（m）,1.25m,1.25m,探索新知,72.6,228.08,400,75.1,235.93,407.85,注：取3.14159,探索新知,85.96m,72.6m,第二道,直径：,周长：,全长：,75.1m,235.93m,407.85m,第三道,直径：,周长：,全长：,75.11.251.25=77.6（m）,77.63.14159243.79（m）,85.962243.79=415.71（m）,1.25m,1.25m,75.1m,探索新知,72.6,2
3、28.08,400,75.1,235.93,407.85,77.6,243.79,415.71,注：取3.14159,探索新知,85.96m,72.6m,第三道,直径：,周长：,全长：,77.6m,243.79m,415.71m,第四道,直径：,周长：,全长：,77.61.251.25=80.1（m）,80.13.14159251.64（m）,85.962251.64=423.56（m）,1.25m,1.25m,77.6m,探索新知,72.6,228.08,400,75.1,235.93,407.85,77.6,243.79,415.71,80.1,251.64,423.56,注：取3.141
4、59,探索新知,85.96m,72.6m,第四道,直径：,周长：,全长：,80.1m,251.64m,423.56m,第五道,直径：,周长：,全长：,80.11.251.25=82.6（m）,82.63.14159259.50（m）,85.962259.5=431.42（m）,探索新知,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：取3.14159,探索新知,85.96m,72.6m,第五道,直径：,周长：,全长：,82.6m,259.5m,431.42m
5、,第六道,直径：,周长：,全长：,82.61.251.25=85.1（m）,85.13.14159267.35（m）,85.962267.35=439.27（m）,探索新知,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：取3.14159,探索新知,85.96m,72.6m,第六道,直径：,周长：,全长：,85.1m,267.35m,439.27m,第七道,直径：,周长：,全长：,85.11.251.25=87.6（m）
6、,87.63.14159275.20（m）,85.962275.2=447.12（m）,探索新知,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：取3.14159,探索新知,85.96m,72.6m,第七道,直径：,周长：,全长：,87.6m,275.2m,447.12m,第八道,直径：,周长：,全长：,87.61.251.25=90.1（m）,90.13.14159283.06（m）
7、,85.962283.06=454.98（m）,探索新知,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：取3.14159,各跑道的起跑线应该相差多少米？,7.85m,/ 7.86m,7.85,7.86,7.85,7.86,7.85,7.85,7.86,探索新知,72.6,228.08,400,75.1,235.93,407.85,77.6,243
8、.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：取3.14159,探索新知,两条直道是一样的，所以只需要看圆的周长。圆的周长是这样算的：,第一道：72.6,第二道：(72.62.5) = 72.62.5,第三道：(75.12.5) = 75.12.5,第四道：(77.62.5) = 77.62.5,第五道：(80.12.5) = 80.12.5,第六道：(82.62.5) = 82.62.5,第七道：(85.12.5) = 85.1
9、2.5,第八道：(87.62.5) = 87.62.5,每一条跑道都在上一条跑道的基础上增加2.5的长度。你能算出2.5是多少米吗？,探索新知,我不用算出每条跑道的长度，也知道它们相差多少米?,终点,起点,200米的跑道，每条道的长度都是它们全长的一半。,第一条：4002=200（m）,第二条：407.852=203.925（m）,第三条：415.712=207.855（m）,第四条：423.562=211.78（m）,第五条：431.422=215.71（m）,每条道相差3.925m或3,39m。所以起跑线应依次提前约3.925m。,200米跑步比赛，跑道宽为1.25米，起跑线应依次提前多少米？,跟踪训练,四、课后小结,这节课你有什么收获？还有什么疑问吗？,课堂小结,谢 谢 观 看！,