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Consider the second order linear equation.

y" - 8y' + 16y = 0.
Find its general solution.

User Rkrzr
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1 Answer

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the general solution of the equation y" - 8y' + 16y = 0 is

y = ye^4x - 2y₀xe^4x.

The general solution of the second order linear equation y" - 8y' + 16y = 0 is

y = C₁e^4x + C₂e²x,

where C₁ and C₂ are arbitrary constants.

We can find this solution by assuming that the solution is of the form y = e^(rx). Substituting this into the equation, we get

r²e^(rx) - 8re^(rx) + 16e^(rx) = 0.

Dividing both sides by e^(rx), we get

r² - 8r + 16 = 0.

Factoring this equation, we get

(r - 4)² = 0.

Therefore, r = 4 is a double root of the equation.

This means that the general solution of the equation is of the form y = (C₁ + C₂x)e^4x, where C₁ and C₂ are arbitrary constants.

To find the constants C₁ and C₂, we can use the fact that the solution must also satisfy the initial conditions y(0) = y₀ and y'(0) = y₁.

Substituting y = (C₁ + C₂x)e^4x into y(0) = y₀, we get

y₀ = (C₁ + 0)e^4·0 = C₁.

Substituting y = (C₁ + C₂x)e^4x into y'(0) = y₁, we get

y₁ = (4C₁ + C₂)e^4·0 = 4C₁.

Solving for C₁, we get C₁ = y₀. Substituting this into y = (C₁ + C₂x)e^4x, we get

y = (y₀ + C₂x)e^4x.

To find C₂, we can differentiate this equation, to find y'.

y' = (C₂ + 4y₀x)e^4x.

Substituting y = (y₀ + C₂x)e^4x and y' = (C₂ + 4y₀x)e^4x into y'' = 8y' - 16y, we get

e^4x(y₀ + C₂x)'' = 8e^4x(C₂ + 4y₀x) - 16e^4x(y₀ + C₂x).

Simplifying this equation, we get

C₂ = -2y₀.

User Qiaosen Huang
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