解题方法
1 . 古希腊的数学家海伦在其著作《测地术》中给出了由三角形的三边长a,b,c计算三角形面积的公式:
,这个公式常称为海伦公式,其中,
.我国南宋著名数学家秦九韶在《数书九章》中给出了由三角形的三边长a,b,c计算三角形面积的公式:
,这个公式常称为“三斜求积”公式.
(1)已知
的三条边分别为
,求
的面积;
(2)利用题中所给信息,证明三角形的面积公式
;
(3)在
中,
,求
面积的最大值.
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/684c13a2cea962fb204256ca433a4d58.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/71d788614f1841b4943b30fe6fd1eff3.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/5ad209824da2aadcf7b5479de68187cc.png)
(1)已知
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/15c0dbe3c080c4c4636c64803e5c1f76.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/51ed8dab1f54de9e1fc65fb53600610c.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/15c0dbe3c080c4c4636c64803e5c1f76.png)
(2)利用题中所给信息,证明三角形的面积公式
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/634fdb49ecc32befaf9ac4ce84ae5a37.png)
(3)在
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/15c0dbe3c080c4c4636c64803e5c1f76.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/3b0eba33aa912c5ce4be622945b0243c.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/15c0dbe3c080c4c4636c64803e5c1f76.png)
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解题方法
2 . 已知
,角
、
、
的对边分别为
、
、
,
、
均在线段
上,
为中线,
为
的平分线.
,求证
;
(2)在(1)的条件下,若
,求
;
(3)若
,求
的取值范围.
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/15c0dbe3c080c4c4636c64803e5c1f76.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/5963abe8f421bd99a2aaa94831a951e9.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/7f9e8449aad35c5d840a3395ea86df6d.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/c5db41a1f31d6baee7c69990811edb9f.png)
![](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/8455657dde27aabe6adb7b188e031c11.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/2a30f3a8b673cc28bd90c50cf1a35281.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/0dc5c9827dfd0be5a9c85962d6ccbfb1.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/03902478df1a55bc99703210bccab910.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/68a83fdd2ba72a2dba0b6b10bb3e06b9.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/7cbce11aa19b8bd2bf6ee5a834e005de.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/14342c5f52a0f5d34f58fc938bfe62a6.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/fe29c42302504e7fd8577dbc7d130ac7.png)
(2)在(1)的条件下,若
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/a5f3e693ef0f9f5ff9aec5bf7480ea18.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/c1311f32edf13f8caee5edb03f24a7ba.png)
(3)若
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/8021ba713186ce728699dadb321a612d.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/e6e490f703eb6c9bb1278c78ebc2d661.png)
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解题方法
3 . 用
分别表示
的三个内角
所对边的边长,
表示
的外接圆半径.
(1)
,求
的长;
(2)在
中,若
是钝角,求证:
;
(3)给定三个正实数
,其中
,问
满足怎样的关系时,以
为边长,
为外接圆半径的
不存在,存在一个或存在两个(全等的三角形算作同一个)?在
存在的情况下,用
表示
.
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/76f0649064a085fb74c997fb507a9b6d.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/15c0dbe3c080c4c4636c64803e5c1f76.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/24e0c10fb103930eabd5fa18e8f9bb06.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/4aa0df7f1e45f9de29e802c7f19a4f64.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/15c0dbe3c080c4c4636c64803e5c1f76.png)
(1)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/06fcf8777e54ba6078e0efe810a355b0.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/f52a58fbaf4fea03567e88a9f0f6e37e.png)
(2)在
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/15c0dbe3c080c4c4636c64803e5c1f76.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/194741f4d2ae7ee44cafca780361446a.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/cd0be39076f8a9425300e88e60ee9052.png)
(3)给定三个正实数
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/0aadb354aceba145fa22173f87a00488.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/d2c659396f6a0f72e213185b1ab2e198.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/0aadb354aceba145fa22173f87a00488.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/1b15bd315b801f71bc30b8d772098614.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/4aa0df7f1e45f9de29e802c7f19a4f64.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/15c0dbe3c080c4c4636c64803e5c1f76.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/15c0dbe3c080c4c4636c64803e5c1f76.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/0aadb354aceba145fa22173f87a00488.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/071a7e733d466949ac935b4b8ee8d183.png)
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4 . 如图,在
中,
.
为等边三角形.
(2)试问当
为何值时,
取得最小值?并求出最小值.
(3)求
的取值范围.
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/15c0dbe3c080c4c4636c64803e5c1f76.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/98f6cab08aec875683b343184a701c7f.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/15c0dbe3c080c4c4636c64803e5c1f76.png)
(2)试问当
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/df64046e91b047037f19e4032e3b6de3.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/68a116fa5c4c6d67aa3454ef87826718.png)
(3)求
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/50eae187c6532ec0abf6fd40b0cc2da6.png)
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解题方法
5 . 在
中,已知
,N是BC的中点,M是
的外心.
(1)若
,求AN的长.
(2)当
变化时,猜一个理想角
,使得易求
的值,并证明对任意的
,
为定值.
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/15c0dbe3c080c4c4636c64803e5c1f76.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/b22c64cfb042014a6b538ab1a0276d14.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/15c0dbe3c080c4c4636c64803e5c1f76.png)
(1)若
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/0fffa3d9c32da53b0ea0c338012ea20c.png)
(2)当
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/7cbce11aa19b8bd2bf6ee5a834e005de.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/7cbce11aa19b8bd2bf6ee5a834e005de.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/1905448d38b7465423fe637d700f1552.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/7cbce11aa19b8bd2bf6ee5a834e005de.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/1905448d38b7465423fe637d700f1552.png)
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解题方法
6 . 在
中,内角
所对的边分别为
,满足
.
(1)求证:
;
(2)若
为锐角三角形,求
的最大值.
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/15c0dbe3c080c4c4636c64803e5c1f76.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/24e0c10fb103930eabd5fa18e8f9bb06.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/76f0649064a085fb74c997fb507a9b6d.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/41f8894773008f2afa921e570bf46481.png)
(1)求证:
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/8904522bf844b61febddc24346f8232f.png)
(2)若
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/15c0dbe3c080c4c4636c64803e5c1f76.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/42b39c8104287dd6f46b88fc966e04cb.png)
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7 . 如图,在平面四边形ABCD中,已知
,
,
为等边三角形,记
,
.
,求
的面积;
(2)证明:
;
(3)若
,求
的面积的取值范围.
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/3f4aca5534bce25acaeb7379deed8f8f.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/833cfda415649b832cc136caed392753.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/15c0dbe3c080c4c4636c64803e5c1f76.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/3202b1d9f838c32ab5765ce647d96b6e.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/9940f9f7b1e9a26ab25527406be4d712.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/e3416881a6f67d05fe6b67787047fc86.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/ab2a2834d80ff574e79eae8ca8d4e94f.png)
(2)证明:
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/9276a56a6c0ed7ecbc4e6e5e19af53b2.png)
(3)若
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/e8c98466484e09a9a4ff6b10785d6715.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/ab2a2834d80ff574e79eae8ca8d4e94f.png)
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解题方法
8 . (1)已知
,
,点
在线段
的延长线上,且
,求点
的坐标;
(2)若
是夹角为
的两个单位向量,求:(i)
的值;(ii)函数
的最小值;
(3)请在以下三个结论中任选一个用向量方法 证明.
①余弦定理;②平行四边形的对角线的平方和等于其四边长的平方和;③三角形的三条中线交于一点.
注:如果选择多个结论分别解答,按第一个解答计分.
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/98b2cc0d2f6d3eee9a33db83e0c0830d.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/4dd8a31b5335186eb1bea5c80cddcfd9.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/dad2a36927223bd70f426ba06aea4b45.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/f52a58fbaf4fea03567e88a9f0f6e37e.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/e490ca1cc66be5a2f1677d243fe093db.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/dad2a36927223bd70f426ba06aea4b45.png)
(2)若
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/b8e8b95a61af300412fc65f846089028.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/be6a6301878fed2a01413020b27310a5.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/58054eff6c328eb401995a81c6e91a54.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/7d65f84320b2cea4c64a8254bbceb250.png)
(3)请在以下三个结论中任选一个用
①余弦定理;②平行四边形的对角线的平方和等于其四边长的平方和;③三角形的三条中线交于一点.
注:如果选择多个结论分别解答,按第一个解答计分.
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9 . 在
中,
.
(1)求
的大小;
(2)若
,求证:
为直角三角形.
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/15c0dbe3c080c4c4636c64803e5c1f76.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/87e963905c55e7bea7af874fb68ccf19.png)
(1)求
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/3818a2c9919d358b4c3713396093822b.png)
(2)若
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/da8607bde1fa6cde631a46e921d959a0.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/15c0dbe3c080c4c4636c64803e5c1f76.png)
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解题方法
10 . 如果三角形的一个内角等于另外一个内角的二倍,我们称这样的三角形为二倍角三角形.设
的内角
,
,
的对边分别为
,
,
,已知
.
(1)证明:
为二倍角三角形;
(2)若
为锐角三角形,且
,求
的取值范围.
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/15c0dbe3c080c4c4636c64803e5c1f76.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/5963abe8f421bd99a2aaa94831a951e9.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/7f9e8449aad35c5d840a3395ea86df6d.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/c5db41a1f31d6baee7c69990811edb9f.png)
![](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/0686cb71d57ae5f7e32afcdb5f735099.png)
(1)证明:
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/15c0dbe3c080c4c4636c64803e5c1f76.png)
(2)若
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/15c0dbe3c080c4c4636c64803e5c1f76.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/6de1d395e6c48c0676a1488a299479d9.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/2c94bb12cee76221e13f9ef955b0aab1.png)
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