Animated Solution for Mathematics - Differential Equations: The function y=f(x) is the solution of the differential equation dxdy+x2−1xy=1−x2x4+2x in (−1,1) satisfying f(0)=0. Then ∫−3/23/2f(x)dx is
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Visualized Solution
Identify the Linear Form
The given differential equation is: dxdy+x2−1xy=1−x2x4+2x
This is a Linear Differential Equation of the form: dxdy+P(x)y=Q(x)
Here, P(x)=x2−1x and Q(x)=1−x2x4+2x
Calculate Integrating Factor (I.F.)
Integrating Factor (I.F.)=e∫P(x)dx
∫P(x)dx=∫x2−1xdx
Let u=x2−1⇒du=2xdx
∫2u1du=21ln∣x2−1∣
Simplify the Integrating Factor
Since x∈(−1,1), we have x2<1, so ∣x2−1∣=1−x2
Therefore, ∫P(x)dx=21ln(1−x2)=ln1−x2
I.F.=eln1−x2=1−x2
General Solution Setup
The general solution is: y⋅(I.F.)=∫Q(x)⋅(I.F.)dx
Substitute the values: y1−x2=∫(1−x2x4+2x)⋅1−x2dx
Notice how the 1−x2 terms cancel out perfectly!
Simplified integrand: y1−x2=∫(x4+2x)dx
Integrate the Right Hand Side
Integrate the polynomial: ∫(x4+2x)dx=5x5+x2+C
The equation becomes: y1−x2=5x5+x2+C
This represents the family of curves for the differential equation.
Apply Initial Condition f(0)=0
We are given the initial condition: f(0)=0
This means when x=0, y=0.
Substitute into the equation: 0⋅1−0=505+02+C
0=0+0+C⇒C=0
Define the Function f(x)
With C=0, the equation simplifies to: y1−x2=5x5+x2
Isolate y to find the explicit function f(x):
f(x)=1−x25x5+x2
This is the function we need to integrate next.
Set up the Definite Integral
We need to evaluate: I=∫−2323f(x)dx
Substitute f(x): I=∫−23231−x25x5+x2dx
Split the integral into two parts:
I=∫−232351−x2x5dx+∫−23231−x2x2dx
Analyze the Odd Function
Let g(x)=51−x2x5
Check for symmetry: g(−x)=51−(−x)2(−x)5=−51−x2x5=−g(x)
Since g(x) is an odd function, its integral over symmetric limits [−a,a] is zero.
∫−2323g(x)dx=0
Analyze the Even Function
Let h(x)=1−x2x2
Check for symmetry: h(−x)=1−(−x)2(−x)2=1−x2x2=h(x)
Since h(x) is an even function, ∫−aah(x)dx=2∫0ah(x)dx
Thus, I=0+2∫0231−x2x2dx
Trigonometric Substitution
To evaluate I=2∫0231−x2x2dx, use substitution.
Let x=sinθ⇒dx=cosθdθ
Change limits:
When x=0,θ=0
When x=23,θ=3π
Simplify the Trigonometric Integral
Substitute into the integral: I=2∫03π1−sin2θsin2θcosθdθ
Since 1−sin2θ=cosθ:
I=2∫03πcosθsin2θcosθdθ
The cosθ terms cancel out: I=2∫03πsin2θdθ
Use Double Angle Identity
We need to integrate 2sin2θ.
Use the double angle identity: 2sin2θ=1−cos(2θ)
The integral becomes: I=∫03π(1−cos(2θ))dθ
Final Evaluation
Integrate term by term: I=[θ−2sin(2θ)]03π
Apply the upper limit (3π): (3π−2sin(32π))
Apply the lower limit (0): (0−0)=0
Since sin(32π)=23:
I=3π−223=3π−43
Final Answer:3π−43
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The Sigma Insight: Linear Differential Equations
Solution Diagram
Analyzing the Setup
The given differential equation is:
dxdy+x2−1xy=1−x2x4+2x
This expression follows the standard form of a Linear Differential Equation: dxdy+P(x)y=Q(x). By inspection, we identify:
P(x)=x2−1x,Q(x)=1−x2x4+2x
Determining the Integrating Factor
The Integrating Factor (I.F.) is defined as e∫P(x)dx. We compute the integral:
∫P(x)dx=∫x2−1xdx=21ln∣x2−1∣
Given the domain x∈(−1,1), we note that x2<1, which implies x2−1<0. Therefore, ∣x2−1∣=1−x2. The I.F. becomes:
I.F.=eln1−x2=1−x2
Solving the Differential Equation
Multiplying the original differential equation by the I.F. simplifies the expression significantly. The equation becomes:
dxd(y⋅1−x2)=x4+2x
Integrating both sides with respect to x:
y1−x2=∫(x4+2x)dx=5x5+x2+C
Using the initial condition f(0)=0, we find C=0. Thus, the explicit function is:
f(x)=1−x25x5+x2
Final Calculation via Symmetry
We are tasked with evaluating the definite integral I=∫−2323f(x)dx. We split the integral into two parts:
I=∫−232351−x2x5dx+∫−23231−x2x2dx
The first term is an odd function integrated over symmetric limits, which evaluates to 0. The second term is an even function, allowing us to simplify:
I=2∫0231−x2x2dx
Using the substitution x=sinθ, where dx=cosθdθ, the limits change from [0,23] to [0,3π]:
I=2∫03πcosθsin2θcosθdθ=2∫03πsin2θdθ
Applying the identity 2sin2θ=1−cos(2θ):
I=∫03π(1−cos(2θ))dθ=[θ−2sin(2θ)]03π
Evaluating at the boundaries, we obtain the final result: