Calculus Examples

Solve the Differential Equation (dy)/(dx)=-y/(x^2-4x)
Step 1
Separate the variables.
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Step 1.1
Multiply both sides by .
Step 1.2
Simplify.
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Step 1.2.1
Rewrite using the commutative property of multiplication.
Step 1.2.2
Cancel the common factor of .
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Step 1.2.2.1
Move the leading negative in into the numerator.
Step 1.2.2.2
Cancel the common factor.
Step 1.2.2.3
Rewrite the expression.
Step 1.2.3
Factor out of .
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Step 1.2.3.1
Factor out of .
Step 1.2.3.2
Factor out of .
Step 1.2.3.3
Factor out of .
Step 1.3
Rewrite the equation.
Step 2
Integrate both sides.
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Step 2.1
Set up an integral on each side.
Step 2.2
The integral of with respect to is .
Step 2.3
Integrate the right side.
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Step 2.3.1
Since is constant with respect to , move out of the integral.
Step 2.3.2
Write the fraction using partial fraction decomposition.
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Step 2.3.2.1
Decompose the fraction and multiply through by the common denominator.
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Step 2.3.2.1.1
For each factor in the denominator, create a new fraction using the factor as the denominator, and an unknown value as the numerator. Since the factor in the denominator is linear, put a single variable in its place .
Step 2.3.2.1.2
Multiply each fraction in the equation by the denominator of the original expression. In this case, the denominator is .
Step 2.3.2.1.3
Cancel the common factor of .
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Step 2.3.2.1.3.1
Cancel the common factor.
Step 2.3.2.1.3.2
Rewrite the expression.
Step 2.3.2.1.4
Cancel the common factor of .
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Step 2.3.2.1.4.1
Cancel the common factor.
Step 2.3.2.1.4.2
Rewrite the expression.
Step 2.3.2.1.5
Simplify each term.
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Step 2.3.2.1.5.1
Cancel the common factor of .
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Step 2.3.2.1.5.1.1
Cancel the common factor.
Step 2.3.2.1.5.1.2
Divide by .
Step 2.3.2.1.5.2
Apply the distributive property.
Step 2.3.2.1.5.3
Move to the left of .
Step 2.3.2.1.5.4
Cancel the common factor of .
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Step 2.3.2.1.5.4.1
Cancel the common factor.
Step 2.3.2.1.5.4.2
Divide by .
Step 2.3.2.1.6
Move .
Step 2.3.2.2
Create equations for the partial fraction variables and use them to set up a system of equations.
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Step 2.3.2.2.1
Create an equation for the partial fraction variables by equating the coefficients of from each side of the equation. For the equation to be equal, the equivalent coefficients on each side of the equation must be equal.
Step 2.3.2.2.2
Create an equation for the partial fraction variables by equating the coefficients of the terms not containing . For the equation to be equal, the equivalent coefficients on each side of the equation must be equal.
Step 2.3.2.2.3
Set up the system of equations to find the coefficients of the partial fractions.
Step 2.3.2.3
Solve the system of equations.
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Step 2.3.2.3.1
Solve for in .
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Step 2.3.2.3.1.1
Rewrite the equation as .
Step 2.3.2.3.1.2
Divide each term in by and simplify.
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Step 2.3.2.3.1.2.1
Divide each term in by .
Step 2.3.2.3.1.2.2
Simplify the left side.
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Step 2.3.2.3.1.2.2.1
Cancel the common factor of .
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Step 2.3.2.3.1.2.2.1.1
Cancel the common factor.
Step 2.3.2.3.1.2.2.1.2
Divide by .
Step 2.3.2.3.1.2.3
Simplify the right side.
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Step 2.3.2.3.1.2.3.1
Move the negative in front of the fraction.
Step 2.3.2.3.2
Replace all occurrences of with in each equation.
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Step 2.3.2.3.2.1
Replace all occurrences of in with .
Step 2.3.2.3.2.2
Simplify the right side.
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Step 2.3.2.3.2.2.1
Remove parentheses.
Step 2.3.2.3.3
Solve for in .
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Step 2.3.2.3.3.1
Rewrite the equation as .
Step 2.3.2.3.3.2
Add to both sides of the equation.
Step 2.3.2.3.4
Solve the system of equations.
Step 2.3.2.3.5
List all of the solutions.
Step 2.3.2.4
Replace each of the partial fraction coefficients in with the values found for and .
Step 2.3.2.5
Simplify.
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Step 2.3.2.5.1
Multiply the numerator by the reciprocal of the denominator.
Step 2.3.2.5.2
Multiply by .
Step 2.3.2.5.3
Move to the left of .
Step 2.3.2.5.4
Multiply the numerator by the reciprocal of the denominator.
Step 2.3.2.5.5
Multiply by .
Step 2.3.3
Split the single integral into multiple integrals.
Step 2.3.4
Since is constant with respect to , move out of the integral.
Step 2.3.5
Since is constant with respect to , move out of the integral.
Step 2.3.6
The integral of with respect to is .
Step 2.3.7
Since is constant with respect to , move out of the integral.
Step 2.3.8
Let . Then . Rewrite using and .
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Step 2.3.8.1
Let . Find .
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Step 2.3.8.1.1
Differentiate .
Step 2.3.8.1.2
By the Sum Rule, the derivative of with respect to is .
Step 2.3.8.1.3
Differentiate using the Power Rule which states that is where .
Step 2.3.8.1.4
Since is constant with respect to , the derivative of with respect to is .
Step 2.3.8.1.5
Add and .
Step 2.3.8.2
Rewrite the problem using and .
Step 2.3.9
The integral of with respect to is .
Step 2.3.10
Simplify.
Step 2.3.11
Replace all occurrences of with .
Step 2.3.12
Simplify.
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Step 2.3.12.1
Simplify each term.
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Step 2.3.12.1.1
Combine and .
Step 2.3.12.1.2
Combine and .
Step 2.3.12.2
Combine the numerators over the common denominator.
Step 2.3.12.3
Factor out of .
Step 2.3.12.4
Factor out of .
Step 2.3.12.5
Factor out of .
Step 2.3.12.6
Rewrite as .
Step 2.3.12.7
Move the negative in front of the fraction.
Step 2.3.12.8
Multiply by .
Step 2.3.12.9
Multiply by .
Step 2.3.12.10
Use the quotient property of logarithms, .
Step 2.3.13
Reorder terms.
Step 2.4
Group the constant of integration on the right side as .
Step 3
Solve for .
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Step 3.1
Simplify the right side.
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Step 3.1.1
Combine and .
Step 3.2
Move all the terms containing a logarithm to the left side of the equation.
Step 3.3
To write as a fraction with a common denominator, multiply by .
Step 3.4
Simplify terms.
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Step 3.4.1
Combine and .
Step 3.4.2
Combine the numerators over the common denominator.
Step 3.5
Move to the left of .
Step 3.6
Simplify the left side.
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Step 3.6.1
Simplify .
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Step 3.6.1.1
Simplify the numerator.
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Step 3.6.1.1.1
Simplify by moving inside the logarithm.
Step 3.6.1.1.2
Remove the absolute value in because exponentiations with even powers are always positive.
Step 3.6.1.1.3
Use the quotient property of logarithms, .
Step 3.6.1.1.4
Multiply the numerator by the reciprocal of the denominator.
Step 3.6.1.1.5
Combine and .
Step 3.6.1.2
Rewrite as .
Step 3.6.1.3
Simplify by moving inside the logarithm.
Step 3.6.1.4
Use the power rule to distribute the exponent.
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Step 3.6.1.4.1
Apply the product rule to .
Step 3.6.1.4.2
Apply the product rule to .
Step 3.6.1.5
Simplify the numerator.
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Step 3.6.1.5.1
Multiply the exponents in .
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Step 3.6.1.5.1.1
Apply the power rule and multiply exponents, .
Step 3.6.1.5.1.2
Cancel the common factor of .
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Step 3.6.1.5.1.2.1
Cancel the common factor.
Step 3.6.1.5.1.2.2
Rewrite the expression.
Step 3.6.1.5.2
Simplify.
Step 3.7
To solve for , rewrite the equation using properties of logarithms.
Step 3.8
Rewrite in exponential form using the definition of a logarithm. If and are positive real numbers and , then is equivalent to .
Step 3.9
Solve for .
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Step 3.9.1
Rewrite the equation as .
Step 3.9.2
Multiply both sides by .
Step 3.9.3
Simplify the left side.
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Step 3.9.3.1
Cancel the common factor of .
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Step 3.9.3.1.1
Cancel the common factor.
Step 3.9.3.1.2
Rewrite the expression.
Step 3.9.4
Divide each term in by and simplify.
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Step 3.9.4.1
Divide each term in by .
Step 3.9.4.2
Simplify the left side.
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Step 3.9.4.2.1
Cancel the common factor.
Step 3.9.4.2.2
Divide by .
Step 4
Simplify the constant of integration.