Antiderivative Theory Problem A function f is differentiable over its domain and has the following

Alissa Hutchinson

Alissa Hutchinson

Answered question

2022-05-10

Antiderivative Theory Problem
A function f is differentiable over its domain and has the following properties:
1. f ( x + y ) = f ( x ) + f ( y ) 1 f ( x ) f ( y ) .
2. lim h 0 f ( h ) = 0
3. lim h 0 f ( h ) / h = 1.
i) Show that f ( 0 ) = 0.
ii) show that f ( x ) = 1 + [ f ( x ) ] 2 by using the def of derivatives Show how the above properties are involved.
iii) find f(x) by finding the antiderivative. Use the boundary condition from part (i).
So basically I think I found out how to do part 1 because if x + y = 0 then the top part of the fraction will always have to be zero.
part 2 and 3 are giving me trouble. The definition is the limit ( f ( x + h ) f ( x ) ) / h.
So I can set x + y = h and make the numerator equal to f(h)?

Answer & Explanation

Calvin Oneill

Calvin Oneill

Beginner2022-05-11Added 20 answers

Step 1
f ( x ) = f ( x ) f 2 ( x ) f ( h ) 1 f ( x ) f ( h )
Now I'll look at 3). In order to solve the ODE:
d f d x = 1 + f 2
Step 2
We simply separate the parts out to get
d f 1 + f 2 = d x
Thus arctan f = x + C f = tan ( x + C )
Now we see from part a) that f ( 0 ) = 0 so
0 = tan ( 0 + C ) C = arctan 0 = 0
and we get our solution of f ( x ) = tan ( x )
datomerki8a5yj

datomerki8a5yj

Beginner2022-05-12Added 5 answers

Step 1
The first question is much easier than you're making it. If f is differentiable, it has to be continuous. If f is continuous, then f ( 0 ) = lim x 0 f ( x ).
Step 2
For the second question: note that
lim h 0 f ( x + h ) f ( x ) h = lim h 0 1 h ( f ( x + h ) f ( x ) ) = lim h 0 1 h ( f ( x ) + f ( h ) 1 f ( x ) f ( h ) f ( x ) )

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