Show that two primitives/ antiderivatives are related via a constant
Let
I
⊂<!-- ⊂ -->
Leah Pope
Answered question
2022-06-24
Show that two primitives/ antiderivatives are related via a constant Let be an interval. A differentiable function is called a primitive for the function if for all . Show: If and are two primitives for f on I then there is a constant such that , i.e. for all . What we have covered so far is the formal definition of the derivative in terms of the limit:
I do not see how I can prove firsthand that these two functions differ by a constant. I know it to be true from my pre-calculus and calculus experience, but how would one make the argument from an analysis point of view, can someone give me a hint as to where this constant 'appears'. We normally just define and then it would follow immediately that these two functions have the same derivative.
Answer & Explanation
candelo6a
Beginner2022-06-25Added 24 answers
Step 1 Let . We observe that . We claim this means that G(x) is constant. Suppose on the contrary the function is non-constant this means there must exist and where such that . Step 2 We consider [a,b]. Now We apply the mean value theorem to this interval and the function G(x). We get that there must exist a c such that: Which is a contradiction.
We conclude that G(x) is constant. Thus, and differ by a constant .
Alannah Short
Beginner2022-06-26Added 5 answers
Explanation: If are primitives of f, by linearity of differentiation,
Remains to prove that the antiderivative of 0 is a constant function.