linear independence

[evagelos]

CAN somebody, please write down a formula defining the linear independence of the following functions??

{ e^x,e^{2x}}

[Pinu7]

If e^x and e^2x are linearly independent then the equation

ae^x+be^2x=0 must have the only solution a,b=0.

Differentiate to obtain,

ae^x+2be^2x=0

Subtract the first equation from the second to obtain,
be^2x=0
which is true if and only if b=0.
Then it is obvious that a=0.

Therefore, e^x and e^2x are linearly independent.

[g_edgar]

The definition says: if a,b are constants and a e^x + b e^{2x} = 0 for all x, then a = b = 0.

[evagelos]

The definition says: if a,b are constants and a e^x + b e^{2x} = 0 for all x, then a = b = 0.

Would you say that your definition is equivalent to:

for all a,b,x and ae^x + be^{2x}=0 ,then a=b=0 ?

or in a more combact form:

for all a,b,x [ae^x + be^{2x} =0\Longrightarrow ( a=b=0)]

[HallsofIvy]

Would you say that your definition is equivalent to:

for all a,b,x and ae^x + be^{2x}=0 ,then a=b=0 ?

or in a more combact form:

for all a,b,x [ae^x + be^{2x} =0\Longrightarrow ( a=b=0)]
"For all a, b" makes no sense if "a= b= 0".

Just "if, for all x, ae^x + be^{2x}=0 ,then a=b=0" or
"(for all x ae^x + be^{2x} =0)\Longrightarrow ( a=b=0)"

[evagelos]

"For all a, b" makes no sense if "a= b= 0".

Just "if, for all x, ae^x + be^{2x}=0 ,then a=b=0" or
"(for all x ae^x + be^{2x} =0)\Longrightarrow ( a=b=0)"

You mean that a and ,b cannot have any other value apart from zero??

In that case you do not have to prove anything because ae^x + be^2x =0

OR given any a,b,x and if ae^x + be^{2x} =0 ,then you can prove that the only value a and b can take is zero??

[g_edgar]

(\text{for all } x,\; ae^x + be^{2x} =0)\Longrightarrow ( a=b=0)

Incomplete. How about this...

\text{for all } a,\; \text{for all } b\; [(\text{for all } x,\; ae^x + be^{2x} =0)\Longrightarrow ( a=b=0)]

[HallsofIvy]

You mean that a and ,b cannot have any other value apart from zero??

In that case you do not have to prove anything because ae^x + be^2x =0

OR given any a,b,x and if ae^x + be^{2x} =0 ,then you can prove that the only value a and b can take is zero??
Given that ae^x+ be^{2x}= 0 for all x, then, taking x= 0, a+ b= 0. Since ae^x+ be^{2x}= 0 for all x, differentiating with respect to x, ae^x+ 2be^{2x}= 0 for all x and, setting x= 0 again, a+ 2b= 0. Subtracting the first equation from the second, (a+ 2b)- (a+ b)= b= 0. Putting b= 0 in either equation, a= 0. Is that what you are asking?

Incomplete. How about this...

\text{for all } a,\; \text{for all } b\; [(\text{for all } x,\; ae^x + be^{2x} =0)\Longrightarrow ( a=b=0)]
NO!! It makes NO sense say "for all a, a= 0"! "If, for all x, ax= 0, then a= 0." It makes no sense to say "for all a" there.