Math Problem Statement

y´´+6y´+13y=0 ; y1= e−3xcos2x, y2= e−3xsen2x; y(0)=2,y(0)=0

Solution

We are given the second-order linear homogeneous differential equation:

y+6y+13y=0y'' + 6y' + 13y = 0

We also know the general solution to the corresponding homogeneous equation, where y1=e3xcos2xy_1 = e^{-3x} \cos 2x and y2=e3xsin2xy_2 = e^{-3x} \sin 2x are two linearly independent solutions. The general solution to the differential equation can be written as:

y(x)=c1y1+c2y2=c1e3xcos2x+c2e3xsin2xy(x) = c_1 y_1 + c_2 y_2 = c_1 e^{-3x} \cos 2x + c_2 e^{-3x} \sin 2x

where c1c_1 and c2c_2 are constants that we need to determine using the initial conditions. The initial conditions provided are:

  1. y(0)=2y(0) = 2
  2. y(0)=0y'(0) = 0

Step 1: Apply the initial condition y(0)=2y(0) = 2

Substitute x=0x = 0 into the general solution:

y(0)=c1e0cos0+c2e0sin0=c1(1)(1)+c2(1)(0)=c1y(0) = c_1 e^0 \cos 0 + c_2 e^0 \sin 0 = c_1 (1) (1) + c_2 (1) (0) = c_1

So, c1=2c_1 = 2.

Step 2: Differentiate the general solution to find y(x)y'(x)

Now, differentiate y(x)y(x) with respect to xx:

y(x)=ddx(c1e3xcos2x+c2e3xsin2x)y'(x) = \frac{d}{dx} \left( c_1 e^{-3x} \cos 2x + c_2 e^{-3x} \sin 2x \right)

Using the product rule and chain rule:

y(x)=c1(3e3xcos2x2e3xsin2x)+c2(3e3xsin2x+2e3xcos2x)y'(x) = c_1 \left( -3e^{-3x} \cos 2x - 2e^{-3x} \sin 2x \right) + c_2 \left( -3e^{-3x} \sin 2x + 2e^{-3x} \cos 2x \right)

Simplifying:

y(x)=e3x[c1(3cos2x2sin2x)+c2(3sin2x+2cos2x)]y'(x) = e^{-3x} \left[ c_1 (-3 \cos 2x - 2 \sin 2x) + c_2 (-3 \sin 2x + 2 \cos 2x) \right]

Step 3: Apply the initial condition y(0)=0y'(0) = 0

Substitute x=0x = 0 into y(x)y'(x):

y(0)=e0[c1(3cos02sin0)+c2(3sin0+2cos0)]y'(0) = e^0 \left[ c_1 (-3 \cos 0 - 2 \sin 0) + c_2 (-3 \sin 0 + 2 \cos 0) \right]

y(0)=[c1(3120)+c2(30+21)]y'(0) = \left[ c_1 (-3 \cdot 1 - 2 \cdot 0) + c_2 (-3 \cdot 0 + 2 \cdot 1) \right]

0=3c1+2c20 = -3c_1 + 2c_2

Substitute c1=2c_1 = 2 from the earlier step:

0=3(2)+2c20 = -3(2) + 2c_2

0=6+2c20 = -6 + 2c_2

2c2=6c2=32c_2 = 6 \quad \Rightarrow \quad c_2 = 3

Final Solution

Thus, the particular solution to the differential equation is:

y(x)=2e3xcos2x+3e3xsin2xy(x) = 2e^{-3x} \cos 2x + 3e^{-3x} \sin 2x

This is the solution that satisfies the given initial conditions.


Would you like further details or have any questions? Here are five related problems for you to explore:

  1. Solve y+4y+5y=0y'' + 4y' + 5y = 0 with initial conditions y(0)=1y(0) = 1 and y(0)=0y'(0) = 0.
  2. Find the general solution to y2y+5y=0y'' - 2y' + 5y = 0.
  3. Use the method of undetermined coefficients to solve y+6y+13y=10e3xy'' + 6y' + 13y = 10e^{-3x}.
  4. Solve y+9y=0y'' + 9y = 0 and find the solution if y(0)=0y(0) = 0 and y(0)=1y'(0) = 1.
  5. Show that y1=e3xcos2xy_1 = e^{-3x} \cos 2x and y2=e3xsin2xy_2 = e^{-3x} \sin 2x are linearly independent.

Tip: To determine whether two solutions are linearly independent, you can check their Wronskian determinant.

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Math Problem Analysis

Mathematical Concepts

Differential Equations
Linear Homogeneous Equations
Initial Value Problems

Formulas

General solution for linear homogeneous differential equations: y(x) = c1 y1 + c2 y2
Product Rule for derivatives: (uv)' = u'v + uv'
Chain Rule for derivatives: (f(g(x)))' = f'(g(x)) * g'(x)

Theorems

Existence and Uniqueness Theorem for Differential Equations
Linearly Independent Solutions for Homogeneous Differential Equations

Suitable Grade Level

Undergraduate Mathematics or Advanced High School