1 . 对数函数与指数函数的图象与性质.
过点
的切线方程,并画出对数曲线和所求切线的图象.
(2)观察(1)中的图象,你发现切线在切点
附近非常接近曲线吗?当
很小时,你能得出近似公式吗?试用此近似公式计算
以及
的近似值.
(3)再观察(1)中的图象,你可以发现切线
行在曲线
上方,即对所有的
,不等式
恒成立.试通过理论推导证明这个不等式.(提示:求函数
的最小值.)
(4)对数曲线:
关于直线
的轴对称图形
是什么函数的图象?对数曲线的切线的轴对称图形是曲线
的切线吗?试写出它的方程,并判断该切线是在曲线
的上方还是下方.你能得出什么不等式?
(5)为什么对数曲线
在点
处的切线的斜率
“正好”等于1?
因为当
时,
斜率
.
又因为当
,
,因此
.若将对数的底数取
,则切线的斜率
.
试仿此求出曲线
在点
处的切线方程.形式上复杂吗?
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/12be206d66e65eb92ef08bad8cd8f71d.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/1d7a999c36de5c9a9ce876a4a56fa34c.png)
(2)观察(1)中的图象,你发现切线在切点
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/1d7a999c36de5c9a9ce876a4a56fa34c.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/7d99d2f9daf80dfcf2e6c27672d1797d.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/cb9d8d758af3394b9c9e5b78f6857dbe.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/a781ad6d16ef7ac9a003b5c7d88326e5.png)
(3)再观察(1)中的图象,你可以发现切线
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/9e6e15daf7b14dbff32c390f4984dcfb.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/12be206d66e65eb92ef08bad8cd8f71d.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/08115d6d9f876dea921a4d32260ff1fb.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/4123b4b9e76a410c64a08c0a8c134664.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/962b8282ce3b4f4e61401ab0b0d77d0e.png)
(4)对数曲线:
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/12be206d66e65eb92ef08bad8cd8f71d.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/d77f5191798242b7b9b88a75e17e4425.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/46d00236ece53eb4096f2790ac7558d8.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/46d00236ece53eb4096f2790ac7558d8.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/46d00236ece53eb4096f2790ac7558d8.png)
(5)为什么对数曲线
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/12be206d66e65eb92ef08bad8cd8f71d.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/1d7a999c36de5c9a9ce876a4a56fa34c.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/f0a532e15e232cb4b99a8d4d07c89575.png)
因为当
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/cf1e14d47047d48867d2ddfcdab8794c.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/25928dffd91e172e00b53e1f01a03432.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/f0a532e15e232cb4b99a8d4d07c89575.png)
又因为当
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/02c4264ca2802df797282da720572031.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/107bedb79ebd387bf36d380c64f584cf.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/07e1452343fea476c4e1b0b16ca12e0c.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/041a7c8fc017f596542c5e6ec7d1c40b.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/5095a28bb1b91bf6bed9e2cfbd76bb18.png)
试仿此求出曲线
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/03f0fadbe551b0e0eb7bf9440be740b9.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/1d7a999c36de5c9a9ce876a4a56fa34c.png)
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