将一个圆形纸片分成若干份,拼成近似长方形.已知长方形周长41.1厘米,圆形纸片面积是多少?
\u5c06\u4e00\u4e2a\u5706\u7b49\u5206\u6210\u82e5\u5e72\u4efd\u518d\u62fc\u6210\u4e00\u4e2a\u8fd1\u4f3c\u957f\u65b9\u5f62\u957f\u65b9\u5f62\u5468\u957f\u662f41.4\u5398\u7c73\u8fd9\u4e2a\u5706\u7684\u5468\u957f\u548c\u9762\u79ef\u662f\u591a\u5c11\uff1f\u8bbe\u8fd9\u4e2a\u5706\u7684\u534a\u5f84\u4e3aR\u5398\u7c73
\u8fd1\u4f3c\u957f\u65b9\u5f62\u7684\u957f\u7b49\u4e8e\u5706\u7684\u5468\u957f\u7684\u4e00\u534a\uff0c\u662f2\u00d73.14\u00d7R\u00f72\uff1d3.14R\u5398\u7c73
\u8fd1\u4f3c\u6b63\u65b9\u5f62\u7684\u5bbd\u7b49\u4e8e\u5706\u7684\u534a\u5f84\uff0c\u662fR\u5398\u7c73
\uff083.14R+R\uff09\u00d72\uff1d41.4
8.28R\uff1d41.4
R\uff1d5\u5398\u7c73
\u8fd9\u4e2a\u5706\u7684\u5468\u957f
\uff1d2\u00d73.14\u00d75
\uff1d31.4\uff08\u5398\u7c73\uff09
\u8fd9\u4e2a\u5706\u7684\u9762\u79ef
\uff1d3.14\u00d75\u00d75
\uff1d78.5\uff08\u5e73\u65b9\u5398\u7c73\uff09
\u5706\u7684\u534a\u5f84\u4e3a\uff1a41.4\u00f72\u00f7\uff083.14+1\uff09=5\u5398\u7c73
1\u3001\u5706\u7684\u9762\u79ef\uff1a3.14\u00d75²=78.5\u5e73\u65b9\u5398\u7c73
2\u3001\u6bcf\u4e00\u7b49\u4efd\u7684\u5468\u957f\uff1a3.14\u00d75\u00d72\u00f716+5\u00d72\u224811.96\u5398\u7c73
\u6bcf\u4e00\u7b49\u4efd\u7684\u9762\u79ef\uff1a78.5\u00f716\u22484.91\u5e73\u65b9\u5398\u7c73
将一个圆形纸片分成若干份,拼成近似长方形.那么长方形的周长等于圆的周长与两条半径的长度之和，假设圆的半径是r,则长方形的周长（41.1厘米）是2∏r+2r=41.1,求得r≈5cm,根据圆的面积公s=∏r2,圆的面积是3.14×52=78.5（平方厘米）.答：圆形纸片面积是78.5平方厘米。
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绛旓細瑙ｏ細15.7脳2梅3.14梅2=5锛堝帢绫筹級5脳5脳3.14=78.5锛堝钩鏂瑰帢绫筹級绛旓細杩欎釜鍦嗙殑闈㈢Н鏄78.5骞虫柟鍘樼背銆
绛旓細杩欎釜杩戜技闀挎柟褰㈡槸浠ュ渾鍗婂緞R涓哄锛屽渾鐨鍛ㄩ暱鐨勪竴鍗娤R涓洪暱 闀挎柟褰㈢殑鍛ㄩ暱=2R+2蟺R=82.8(cm)R=10(cm)鍦嗙殑闈㈢Н=蟺R²=100蟺鈮314(cm²)
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绛旓細瑙ｇ敱棰樼煡璁惧渾鐨勫崐寰勪负r锛屽垯闀挎柟褰㈢殑瀹戒负r锛岄暱涓合r 鍒欓暱鏂瑰舰鐨勫懆闀夸负2r+2蟺r锛屽渾鐨鍛ㄩ暱涓2蟺r 鐢遍暱鏂瑰舰鐨勫懆闀挎瘮鍦嗙殑鍛ㄩ暱澶8鍘樼背 寰(2r+2蟺r)-2蟺r=8 鍗硆=4 鎵浠ュ渾鐨勫懆闀夸负2蟺r=8蟺=25.12cm 鏁呮湰棰樺～鍐25.12cm
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绛旓細12.56脳2梅锛3.14脳2锛=4dm 4脳4脳3.14=50.24dm2
绛旓細璁惧渾鐨勫崐寰勪负r 闀挎柟褰㈢殑鍛ㄩ暱=2r+2蟺r=2(1+蟺)r鈮2脳(1+3.14)脳r=8.28r 24.84cm=8.28r r=3cm 鍦嗗舰绾哥墖鐨勯潰绉=蟺r²=3²蟺=9脳3.14=28.26骞虫柟鍘樼背
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绛旓細鍥炵瓟锛24.84闄や互3.14
