阅读下面材料
一个含有多个字母的式子中,如果任意交换两个字母的位置,式子的值都不变,这样的式子就叫做对称式,例如:
;含有两个字母a,b的对称式的基本对称式是
和
,像
等对称式都可以用
,
表示,例如
,请根据以上材料解决下列问题:
(1)式子①
,②
,③
,④
中,属于对称式的是 (填序号);
(2)已知![](https://staticzujuan.xkw.com/quesimg/Upload/formula/5e11def67b89daf5e8c39bc2ae0e9c4a.png)
①若
,求对称式
的值;
②若
,求对称式
的最小值,写出求解过程;
③若
,直接写出对称式
的最大值 .
一个含有多个字母的式子中,如果任意交换两个字母的位置,式子的值都不变,这样的式子就叫做对称式,例如:
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/66fff7dfcac43c6bf39070b7d3ba41e3.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/20d6fc9b90f370fbb27552876b650f8f.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/18f0281e6bbdbe08beeccb55adf84536.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/b6c4cc8d876ee24977f12f1d06c70cc6.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/20d6fc9b90f370fbb27552876b650f8f.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/18f0281e6bbdbe08beeccb55adf84536.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/fd4dc32592ecf1e40491c970fed52b61.png)
(1)式子①
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/dc26b258e0552cf43a3417d4470f37c3.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/7f7266b2ef457b8ddeee3fa2cc24022e.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/a09ffc1644c7029219b88232145abbdf.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/7a977414a3ad65caf5eee28e0cd175de.png)
(2)已知
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/5e11def67b89daf5e8c39bc2ae0e9c4a.png)
①若
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/e21cc28ce492709915dc50f3e5f0f4cd.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/86c5b46e81044efa7090be7ae678ff72.png)
②若
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/db50504026e8b8e99e380b32a84b1b4e.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/b1def6b4adcda5a71ba0fab52ad91222.png)
③若
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/e94f16d5ed858699bfea5039a7bf8ae6.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/594e5e87a8fd507777de4165d5fdfc25.png)
23-24八年级上·福建福州·期中 查看更多[4]
福建省福州市鼓楼区屏东中学2023-2024学年八年级上学期期中模拟数学试题(已下线)15.1分式1(题型精练)(已下线)15.1分式2(题型精练)福建省泉州台商投资区2023-2024学年八年级上学期期中数学试题
更新时间:2023-10-15 18:27:57
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解答题-问答题
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【推荐1】一个边长为
的正方形纸片(如图1)上剪去两个相同的小长方形,得到一个对数视力表中的“
”的图案(如图2),再将剪下的两个小长方形拼成一个新长方形(如图3).
![](https://img.xkw.com/dksih/QBM/editorImg/2024/1/23/b6358e0b-e0a0-478b-a149-c0498916b9af.jpg?resizew=306)
(1)用含有
,
的式子表示新长方形的长是________,宽是________;
(2)若空白缺口的宽度与
相等,用含有
的代数式表示黑色字母“
”的周长.
(3)当
时,求黑色字母“
”的周长.
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/0a6936d370d6a238a608ca56f87198de.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/2a30f3a8b673cc28bd90c50cf1a35281.png)
![](https://img.xkw.com/dksih/QBM/editorImg/2024/1/23/b6358e0b-e0a0-478b-a149-c0498916b9af.jpg?resizew=306)
(1)用含有
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/0a6936d370d6a238a608ca56f87198de.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/2c94bb12cee76221e13f9ef955b0aab1.png)
(2)若空白缺口的宽度与
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/2c94bb12cee76221e13f9ef955b0aab1.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/0a6936d370d6a238a608ca56f87198de.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/2a30f3a8b673cc28bd90c50cf1a35281.png)
(3)当
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/0b118c1b63de3f133d270daedf15e2e5.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/2a30f3a8b673cc28bd90c50cf1a35281.png)
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【推荐2】若
、
互为相反数,
、
互为倒数,
的绝对值是最小的正整数,求
的值.
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/0a6936d370d6a238a608ca56f87198de.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/2c94bb12cee76221e13f9ef955b0aab1.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/071a7e733d466949ac935b4b8ee8d183.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/5c02bc0c74292b1e8f395f90935d3174.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/294f5ba74cdf695fc9a8a8e52f421328.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/1c7f8157b5bb0e0a351d62be14e59c4d.png)
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解答题-计算题
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【推荐1】阅读材料:
求
的值.
解:设
.①
将等式①的两边同乘2,得
.②
②-①得,![](https://staticzujuan.xkw.com/quesimg/Upload/formula/a5a735c11777fac1180bc178b3395e69.png)
即![](https://staticzujuan.xkw.com/quesimg/Upload/formula/851b50d131448d404fd488663ed29259.png)
即![](https://staticzujuan.xkw.com/quesimg/Upload/formula/9085340c133394cc03d4e5fd9e81b4dc.png)
请仿照此法计算:
(1)直接写出
的值为______;
(2)求
的值;
(3)求
的值.
求
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/13802fa461e7732d335ade28a7a51939.png)
解:设
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/6293d64ded836bf09e48907cdef8e2bf.png)
将等式①的两边同乘2,得
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/6fe32b1565e0fef06ff70e670f488a82.png)
②-①得,
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/a5a735c11777fac1180bc178b3395e69.png)
即
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/851b50d131448d404fd488663ed29259.png)
即
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/9085340c133394cc03d4e5fd9e81b4dc.png)
请仿照此法计算:
(1)直接写出
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/8c1a703bc28dec60e5d30e0b926afb17.png)
(2)求
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/35b56e4aaa8aac7c9715d3614df21025.png)
(3)求
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/9d2e9508f1a4a81c21f56cb5efb067f2.png)
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【推荐2】如图,平面内有公共端点的六条射线
,
,
,
,
,
,从射线
开始按逆时针方向依次在射线上写出数字1,2,3,4,5,6,7,….
![](https://img.xkw.com/dksih/QBM/editorImg/2023/2/15/43a70ed4-357e-497a-8214-561be3a149ae.png?resizew=221)
(1)数“
”在射线______上;
(2)请任意写出三条射线上数的排列规律(用含有正整数n的式子表示);
(3)数“
”在射线
上吗?说明理由.
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/ef4113c492885ba7c47fe42ac792578f.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/b90e0f35eda1a729fed485f83da5ea9d.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/828628c0876b45381c9a0edeb0fec236.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/683c590673eece14fea3319c4fd5eb55.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/a299d2b999568e80be8005565ba209a4.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/6cad4595d5352b2884568a59d8d766a4.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/ef4113c492885ba7c47fe42ac792578f.png)
![](https://img.xkw.com/dksih/QBM/editorImg/2023/2/15/43a70ed4-357e-497a-8214-561be3a149ae.png?resizew=221)
(1)数“
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/ea1834490aacbee800ed5721312f4be1.png)
(2)请任意写出三条射线上数的排列规律(用含有正整数n的式子表示);
(3)数“
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/4d01dd350dc95f42f1883e0cc7aae084.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/b90e0f35eda1a729fed485f83da5ea9d.png)
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【推荐1】阅读下列材料:利用完全平方公式,将多项式
变形为
的形式,然后由
就可求出多项式
的最小值.
例题:求
的最小值
解:![](https://staticzujuan.xkw.com/quesimg/Upload/formula/5f0182b95d5ea5ad71734199dd63d01b.png)
∵不论x取何值,
总是非负数,即
.
∴![](https://staticzujuan.xkw.com/quesimg/Upload/formula/3bfa96b1e04d4f203cd90a525c987615.png)
∴当
时,
有最小值,最小值是1.
(1)填空:![](https://staticzujuan.xkw.com/quesimg/Upload/formula/bd33a11da43794c29197652f4bdf6039.png)
(2)将
变形为
的形式,并求出
的最小值.
(3)如图所示的第一个长方形边长分别是
、
,面积为
,如图所示的第二个长方形边长分别是
、
,面积为
,试比较
与
的大小,并说明理由.
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/479fbc4acd0fa10e20145a71ce9a98d3.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/0e156c1f2bb7fdeb24a547b393ecd76f.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/5ba0ec56806823eab555e8c29192f6eb.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/479fbc4acd0fa10e20145a71ce9a98d3.png)
例题:求
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/fbaf11d37bf9ffcab82d40a87b2810ea.png)
解:
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/5f0182b95d5ea5ad71734199dd63d01b.png)
∵不论x取何值,
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/f0937aaef88155fb6c1991d7bb16f14f.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/5c189ece8540aeb0561642cdc6914036.png)
∴
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/3bfa96b1e04d4f203cd90a525c987615.png)
∴当
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/39cc033406da2cdd342308972c6701f1.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/fbaf11d37bf9ffcab82d40a87b2810ea.png)
(1)填空:
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/bd33a11da43794c29197652f4bdf6039.png)
(2)将
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/4b12f0507cae6821a61ae1c2a3b1b321.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/0e156c1f2bb7fdeb24a547b393ecd76f.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/4b12f0507cae6821a61ae1c2a3b1b321.png)
(3)如图所示的第一个长方形边长分别是
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/35870d060643b20dc3c83f692300441b.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/e7b4d3176035989318ed293c25fe6369.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/e097c8d4c948de063796bd19f85b3a9a.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/ad52beba3181bfc922d5c59d73a5a11a.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/7fbb9c306da912756c1292f5a9988d91.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/1e0bd63f55069a3bc870915010b39225.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/e097c8d4c948de063796bd19f85b3a9a.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/1e0bd63f55069a3bc870915010b39225.png)
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