If F(x) and G(x) both solve the same initial value problem, then is it true that F(x)=G(x)?

Sasha Hess

Sasha Hess

Answered question

2022-09-05

If F(x) and G(x) both solve the same initial value problem, then is it true that F(x)=G(x)?

Answer & Explanation

Hofpoetb9

Hofpoetb9

Beginner2022-09-06Added 17 answers

We have :
y=F(x) and y=G(x) both satisfy d y d x = f ( x ) and y ( x 0 ) = y 0
Consider y=F(x)
It satisfies the equation:
d y d x = f ( x ) d d x ( F ( x ) = f ( x )
Hence F(x) is an antiderivative of f(x) and by the FTC, we have:
y f =   f ( x )   d x
y f = F ( x ) + A
Using an identical argument for G(x) we also have:
y g = G ( x ) + B
And using the initial condition
y ( x 0 ) = y 0 F ( x 0 ) = G ( x 0 ) = y 0
So we have:
y 0 = F ( x 0 ) + A = y 0 + A A = 0
y 0 = G ( x 0 ) + B = y 0 + B B = 0
And we therefore conclude that
y f = y g F ( x ) = G ( x )
ie the solution to a First Order Differential Equation is Unique

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