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**MathsIsFun****Administrator**- Registered: 2005-01-21
- Posts: 7,535

Differential Calculus Formulas

"The physicists defer only to mathematicians, and the mathematicians defer only to God ..." - Leon M. Lederman

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**Ricky****Moderator**- Registered: 2005-12-04
- Posts: 3,791

"In the real world, this would be a problem. But in mathematics, we can just define a place where this problem doesn't exist. So we'll go ahead and do that now..."

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**George,Y****Member**- Registered: 2006-03-12
- Posts: 1,306

--solving procedure

p(t) could any function without y, constant is ok.

Linear means no y, y[sup]2[/sup] or yy', etc.

So virtually there are only y and y' multiplied by function of t or constant, function of t, and constant are allowed in the 1st Order Linear DE. And the DEs satisfying this condition can be easily transformed into the standard form above through division.

*Last edited by George,Y (2007-05-21 16:22:02)*

**X'(y-Xβ)=0**

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**ganesh****Moderator**- Registered: 2005-06-28
- Posts: 13,819

**Derivatives of some Elelmentary functions**

Derivative of a constant is zero.

If u and v are functions of x, and c is a constant,

provided v≠0Character is who you are when no one is looking.

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**ganesh****Moderator**- Registered: 2005-06-28
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Chain rule

Inverse Function

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**ganesh****Moderator**- Registered: 2005-06-28
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**Inverse Trignometric Functions**

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**ganesh****Moderator**- Registered: 2005-06-28
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**nth derivative**

**Leibnitz theorem**

If u and v are functions of x and n is a positive integer, then

Character is who you are when no one is looking.

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**ganesh****Moderator**- Registered: 2005-06-28
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**Hyperbolic functions**

**Inverse Hyperbolic functions**

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**ganesh****Moderator**- Registered: 2005-06-28
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**Derivatives of functions of the form (x² ± a²)**

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**ganesh****Moderator**- Registered: 2005-06-28
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**Tangents and Normals**

If y=f(x) is a curve,

If dy/dx=0 at a point P, then the slope of the tangent at P is zero, therefore, the tangent is parallel to the x-axis.

If dy/dx = infinity at a point P, then the slope of the tangent at P is infinity, therefore, the tangent is parallel to the y-axis.

Equations of tangent and normal at a point:-

Slope of the tangent at point P (x1, y1) on the curve y=f(x) is the value of dy/dx at (x1,y1). Let dy/dx=m at (x1,y1).

Then the equation of the tangent at (x1,y1) is

Normal at point P is perpendicular to the tangent at P and passes through P(x1,y1).

Therefore,

Equation of the normal at P(x1,y1) is

**Angle between two curves**

The angle between two curves is the angle between the tangents to the curves at the point of intersection.

Let

be the equations of two curves C1 and C2 intersecting at P.

Then, the slope of tangent at P to the first curve is given by

Similarly, the slope of the tangent to the second curve is given by

Then, the angle between the curves is given by

or

If m1=m2, then the curves touch each other at P.

If m1m2=-1, then the curves cut each other orthogonally at P.

Character is who you are when no one is looking.

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**Zhylliolom****Real Member**- Registered: 2005-09-05
- Posts: 412

**Derivative of a Parametric Function**

The derivative of a parametric function defined by x = f(t) and y = g(t) is given by

**L'Hôpital's Rule**

For differentiable functions f(x) and g(x),

This is useful for determining limits which give indeterminate forms such as 0/0, ∞/∞, 0[sup]0[/sup], 1[sup]∞[/sup], 0 × ∞, ∞ - ∞, and ∞[sup]0[/sup].

**Local Extrema (Maxima and Minima)**

The point a on a curve f(x) is a local maximum if f'(a) = 0 and f''(a) < 0.

The point a on a curve f(x) is a local minimum if f'(a) = 0 and f''(a) > 0.

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**Zhylliolom****Real Member**- Registered: 2005-09-05
- Posts: 412

**The Laplace Transform**

The Laplace transform is a useful tool for solving differential equations. The Laplace transform F(s) of f(x) is defined by

The Laplace transform is a linear operator, and thus

The inverse Laplace transform

is also a linear operator:

**Solution of a Linear Differential Equation of Constant Coefficients using a Laplace Transform**

Consider the linear differential equation

Taking the Laplace transform of both sides, and noting that

we may write the differential equation as

or, collecting coefficients,

Now, given that we have the initial conditions at x = 0, we can proceed to solve for L[y], and once we have an equation for L[y], we may simplify it (often by means of partial fractions) and then find the inverse Laplace transform, and thus find y. If initial conditions are given at some x[sub]0[/sub] ≠ 0, let u = x - x[sub]0[/sub] and solve the differential equation in terms of u, then substitute the value of x back in when the solution is finished.

**List of Selected Laplace Transforms**

*Note: Taking the inverse Laplace transform of these equations will give an expression for the inverse Laplace transform of a function F(s).*

*Feel free to request any other Laplace transforms/inverse Laplace transforms. I have about 150 other transforms for a wide variety of cases, but they seem too obscure for posting.*

*Example problems may be posted on request to aid in clarity.*

*Last edited by Zhylliolom (2006-08-06 22:03:52)*

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**Manta****Member**- Registered: 2008-12-30
- Posts: 1

:lol::lol: i am very obseded by those functions[integral,derivative,trigonometry,etc... even if i have some difficulties in some of them] and calculus even if i have difficulties understanding some of them(i am only 12 years old).I also loved quadratic equations when i was younger.

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**wailinaung****Member**- Registered: 2010-05-20
- Posts: 1

differentional equation problems y'=x^x how to solve? and y'=(arctgx)^x how to solve?

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**bobbym****Administrator**- From: Bumpkinland
- Registered: 2009-04-12
- Posts: 85,204

Hi wailinaung;

y'=x^x Since the variables are already separated for you you just need to integrate both sides. Offhand I do not know how to integrate x^x. Same goes for integrating arctan(x)^x.

Checking pierce's table of integrals neither of them is there. Googling says they cannot be integrated in terms of elementary functions. So solving those DE's is out. You can get an approximation to them by series methods and also if you are given a numerical initial condition, by numerical methods.

**In mathematics, you don't understand things. You just get used to them.Of course that result can be rigorously obtained, but who cares?Combinatorics is Algebra and Algebra is Combinatorics.**

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**hariprasath2****Member**- Registered: 2010-09-21
- Posts: 1

ganesh wrote:

Derivatives of some Elelmentary functionsDerivative of a constant is zero.

If u and v are functions of x, and c is a constant,

provided v≠0

:(thank u ganesh

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