数学代写|微积分代写Calculus代写|The Derivative of $a^u$

Doug I. Jones

Doug I. Jones

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如果你也在 怎样代写微积分Calculus 这个学科遇到相关的难题,请随时右上角联系我们的24/7代写客服。微积分Calculus 最初被称为无穷小微积分或 “无穷小的微积分”,是对连续变化的数学研究,就像几何学是对形状的研究,而代数是对算术运算的概括研究一样。

微积分Calculus 它有两个主要分支,微分和积分;微分涉及瞬时变化率和曲线的斜率,而积分涉及数量的累积,以及曲线下或曲线之间的面积。这两个分支通过微积分的基本定理相互关联,它们利用了无限序列和无限数列收敛到一个明确定义的极限的基本概念 。17世纪末,牛顿(Isaac Newton)和莱布尼兹(Gottfried Wilhelm Leibniz)独立开发了无限小数微积分。后来的工作,包括对极限概念的编纂,将这些发展置于更坚实的概念基础上。今天,微积分在科学、工程和社会科学中得到了广泛的应用。

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数学代写|微积分代写Calculus代写|The Derivative of $a^u$

数学代写|微积分代写Calculus代写|The Derivative of $a^u$

To find this derivative, we start with the defining equation $a^x=e^{x \ln a}$. Then we have
$$
\begin{aligned}
\frac{d}{d x} a^x & =\frac{d}{d x} e^{x \ln a}=e^{x \ln a} \cdot \frac{d}{d x}(x \ln a) \quad \frac{d}{d x} e^u=e^u \frac{d u}{d x} \
& =a^x \ln a .
\end{aligned}
$$
We now see why $e^x$ is the exponential function preferred in calculus. If $a=e$, then $\ln a=1$ and the derivative of $a^x$ simplifies to
$$
\frac{d}{d x} e^x=e^x \ln e=e^x . \quad \ln e=1
$$
With the Chain Rule, we get the following form for the derivative of the general exponential function.
If $a>0$ and $u$ is a differentiable function of $x$, then $a^u$ is a differentiable function of $x$ and
$$
\frac{d}{d x} a^u=a^u \ln a \frac{d u}{d x}
$$
The integral equivalent of this last result gives the general antiderivative
$$
\int a^u d u=\frac{a^u}{\ln a}+C
$$
From Equation (3) with $u=x$, we see that the derivative of $a^x$ is positive if $\ln a>0$, or $a>1$, and negative if $\ln a<0$, or $01$ and a decreasing function of $x$ if $0<a<1$. In each case, $a^x$ is one-to-one. The second derivative
$$
\frac{d^2}{d x^2}\left(a^x\right)=\frac{d}{d x}\left(a^x \ln a\right)=(\ln a)^2 a^x
$$
is positive for all $x$, so the graph of $a^x$ is concave up on every interval of the real line. Figure 7.13 displays the graphs of several exponential functions.

数学代写|微积分代写Calculus代写|Logarithms with Base a

If $a$ is any positive number other than 1 , the function $a^x$ is one-to-one and has a nonzero derivative at every point. It therefore has a differentiable inverse. We call the inverse the logarithm of $x$ with base $a$ and denote it by $\log a x$. DEFINITION For any positive number $a \neq 1$, $\log _a x$ is the inverse function of $a^x$. The graph of $y=\log _a x$ can be obtained by reflecting the graph of $y=a^x$ across the $45^{\circ}$ line $y=x$ (Figure 7.14). When $a=e$, we have $\log _e x=$ inverse of $e^x=\ln x$. (The function $\log {10} x$ is sometimes written simply as $\log x$ and is called the common logarithm of $x$.) Since $\log _a x$ and $a^x$ are inverses of one another, composing them in either order gives the identity function.
Inverse Equations for $a^x$ and $\log _a x$
$$
\begin{aligned}
a^{\log _a x} & =x & & (x>0) \
\log _a\left(a^x\right) & =x & & (\text { all } x)
\end{aligned}
$$
The function $\log _a x$ is actually just a numerical multiple of $\ln x$. To see this, we let $y=\log _a x$ and then take the natural logarithm of both sides of the equivalent equation $a^y=x$ to obtain $y \ln a=\ln x$. Solving for $y$ gives
$$
\log _a x=\frac{\ln x}{\ln a}
$$

数学代写|微积分代写Calculus代写|The Derivative of $a^u$

微积分代考

数学代写|微积分代写Calculus代写|The Derivative of $a^u$

为了求这个导数,我们从定义方程$a^x=e^{x \ln a}$开始。然后我们有
$$
\begin{aligned}
\frac{d}{d x} a^x & =\frac{d}{d x} e^{x \ln a}=e^{x \ln a} \cdot \frac{d}{d x}(x \ln a) \quad \frac{d}{d x} e^u=e^u \frac{d u}{d x} \
& =a^x \ln a .
\end{aligned}
$$
现在我们明白了为什么$e^x$是微积分中首选的指数函数。如果是$a=e$,那么$\ln a=1$, $a^x$的导数化简为
$$
\frac{d}{d x} e^x=e^x \ln e=e^x . \quad \ln e=1
$$
利用链式法则,我们得到一般指数函数的导数的如下形式。
如果$a>0$和$u$是$x$的可微函数,则$a^u$是$x$和的可微函数
$$
\frac{d}{d x} a^u=a^u \ln a \frac{d u}{d x}
$$
最后一个结果的积分等价给出了一般不定积分
$$
\int a^u d u=\frac{a^u}{\ln a}+C
$$
由方程(3)与$u=x$,我们看到$a^x$的导数是正的,如果$\ln a>0$,或$a>1$,如果$\ln a<0$,或$01$,和$x$的一个递减函数$0<a<1$。在每种情况下,$a^x$都是一对一的。二阶导数
$$
\frac{d^2}{d x^2}\left(a^x\right)=\frac{d}{d x}\left(a^x \ln a\right)=(\ln a)^2 a^x
$$
对所有$x$都是正的,所以$a^x$的图像在实线的每一个区间上都是上凹的。图7.13显示了几个指数函数的曲线图。

数学代写|微积分代写Calculus代写|Logarithms with Base a

如果$a$是除1以外的任何正数,则函数$a^x$是一对一的,并且在每个点上都有非零导数。因此它有一个可微逆。我们称以$a$为底的$x$的逆对数为$\log a x$。对于任意正数$a \neq 1$, $\log _a x$是$a^x$的反函数。将$y=a^x$在$45^{\circ}$线$y=x$上的图形反映出来,即可得到$y=\log _a x$的图形(图7.14)。当$a=e$时,我们有$e^x=\ln x$的$\log _e x=$逆。(函数$\log {10} x$有时简写为$\log x$,称为$x$的公共对数。)因为$\log _a x$和$a^x$互为反比,所以以任意一种顺序组合它们就得到了恒等函数。
$a^x$和$\log _a x$的反方程
$$
\begin{aligned}
a^{\log _a x} & =x & & (x>0) \
\log _a\left(a^x\right) & =x & & (\text { all } x)
\end{aligned}
$$
函数$\log _a x$实际上是$\ln x$的数值倍。要看这个,我们让$y=\log _a x$,然后对等价方程$a^y=x$两边取自然对数,得到$y \ln a=\ln x$。求解$y$得到
$$
\log _a x=\frac{\ln x}{\ln a}
$$

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