- #1
OmniNewton
- 105
- 5
Homework Statement
Prove that if f'(x) = g'(x) for all x in an interval (a,b) then f-g is constant on (a,b) then f-g is constant on (a,b) that is f(x) = g(x) + C
Homework Equations
Let C be a constant
Let D be a constant
The Attempt at a Solution
f(x) = antiderivative(f'(x)) = f(x) + C
g(x)= antiderivative(g'(x)) = g(x) + D
f-g = f(x) + C - (g(x) + D)
f-g = f(x) - g(x) + C - D
but since f'(x) = g'(x) then f(x) = g(x) the only difference is their constant.
then,
f-g = f(x) - f(x) + C - D
f-g = C - D
Since C and D are constants
then,
f-g = constant
if C = D
then f-g = 0
Note: I feel like I proved it but my notation is wrong since I cannot use f(x) = f(x) + C. I would like guidance for the proper notation to use. The possibility also exists my proof is completely wrong. I would like help
Thanks in Advanced!