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Encyclopedia > Derivative (examples)

Contents

Example 1

Consider f(x) = 5:

f'(x)=lim_{hrightarrow 0} frac{f(x+h)-f(x)}{h} = lim_{hrightarrow 0} frac{f(x+h)-5}{h} = lim_{hrightarrow 0} frac{(5-5)}{h} = lim_{hrightarrow 0} frac{0}{h} = lim_{hrightarrow 0} 0 = 0

The derivative of a constant function is zero. In mathematics a constant function is a function whose values do not vary and thus are constant. ... 0 (zero) is both a number and a numerical digit used to represent that number in numerals. ...


Example 2

Consider the graph of f(x) = 2x − 3. If the reader has an understanding of algebra and the Cartesian coordinate system, the reader should be able to independently determine that this line has a slope of 2 at every point. Using the above quotient (along with an understanding of the limit, secant, and tangent) one can determine the slope at (4,5): Algebra is a branch of mathematics concerning the study of structure, relation and quantity. ... Fig. ... Three lines — the red and blue lines have same slope, while the red and green ones have same y-intercept. ... In mathematics, the concept of a limit is used to describe the behavior of a function as its argument either gets close to some point, or as it becomes arbitrarily large; or the behavior of a sequences elements, as their index increases indefinitely. ... Secant is a term in mathematics. ... In mathematics, the word tangent has two distinct but etymologically-related meanings: one in geometry and one in trigonometry. ...

begin{align} f'(4) &= lim_{hto 0}frac{f(4+h)-f(4)}{h}  &= lim_{hto 0}frac{2(4+h)-3-(2cdot 4-3)}{h}  &= lim_{hto 0}frac{8+2h-3-8+3}{h}  &= lim_{hto 0}frac{2h}{h}  &= 2 end{align}

The derivative and slope are equivalent.


Example 3

Via differentiation, one can find the slope of a curve. Consider f(x) = x2:

f'(x), = lim_{hrightarrow 0}frac{f(x+h)-f(x)}{h}
= lim_{hrightarrow 0}frac{(x+h)^2 - x^2}{h}
= lim_{hrightarrow 0}frac{x^2 + 2xh + h^2 - x^2}{h}
= lim_{hrightarrow 0}frac{2xh + h^2}{h}
= lim_{hrightarrow 0}(2x + h) = 2x

For any point x, the slope of the function f(x) = x2 is f'(x) = 2x.


Example 4

Consider f(x) = sqrt{x}:

f'(x), = lim_{hrightarrow 0}frac{f(x+h)-f(x)}{h}
= lim_{hrightarrow 0}frac{sqrt{x+h} - sqrt{x}}{h}
= lim_{hrightarrow 0}left(frac{sqrt{x+h} - sqrt{x}}{h}right) left(frac{sqrt{x+h} + sqrt{x}}{sqrt{x+h} + sqrt{x}}right)
= lim_{hrightarrow 0}frac{x+h - x}{h(sqrt{x+h} + sqrt{x})}
= lim_{hrightarrow 0}frac{1}{sqrt{x+h} + sqrt{x}}
= frac{1 }{2 sqrt{x}}

Example 5

The same as the previous example, but now we search the derivative of the derivative.
Consider f(x) = sqrt{x}:

Failed to parse (unknown error): begin{align} f''(x) &= lim_{hto 0}frac{f'(x+h)-ftest &= lim_{hto 0} frac{left(frac{1}{2 sqrt{x+h}}-frac{1}{2 sqrt{x}}right)(2 sqrt{x+h}+2 sqrt{x})}{h(2 sqrt{x+h}+2 sqrt{x})} &= -frac{1}{4 x sqrt{x}} end{align} hacked by godzilla

  Results from FactBites:
 
Derivative - Wikipedia, the free encyclopedia (2210 words)
If the second derivative is positive at a critical point, that point is a local minimum; if negative, it is a local maximum; if zero, it may or may not be a local minimum or local maximum.
The common thread is that the derivative at a point serves as a linear approximation of the function at that point.
Perhaps the most natural situation is that of functions between differentiable manifolds; the derivative at a certain point then becomes a linear transformation between the corresponding tangent spaces and the derivative function becomes a map between the tangent bundles.
Derivative - definition of Derivative in Encyclopedia (2042 words)
The derivative of a function at a certain point is a measure of the rate at which that function is changing as an argument undergoes change.
The derivative of f(x) is written in several possible ways: f ′(x) (pronounced f prime of x), d/dx[f(x)] (pronounced d by d x of f of x or d d x of f of x), df/dx (pronounced d f by d x or d f d x), or D
Derivatives are defined by taking the limit of the slope of secant lines as they approach a tangent line.
  More results at FactBites »


 

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