Let be the set of real numbers. Determine all functions that satisfy the equationfor all real numbers and .
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Let be the set of real numbers. Determine all functions that satisfy the equationfor all real numbers and .
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To solve the functional equation:
for all , we start by considering particular values for and to simplify the equation and gain insight into the form of the function .
### Step 1: Substitute
Let . The equation becomes:
### Step 2: Substitute
Let . The equation becomes:
### Step 3: Simplifying with substitutions
From the equation in Step 2, we can rearrange it as:
Now, let's analyze the behavior of given different hypothetical forms:
#### Case 1: Assume is linear of the form .
Substitute into the original equation:
Equating both sides for all , we get:
- Coefficient of gives: implying or .
- Coefficient of :
- Constant terms and linear terms need to match.
#### Subcase 1.1:
If , substituting back gives contradictions unless , hence one solution is:
#### Subcase 1.2:
If , substitute back to verify consistency. However, checking individual substitutions lead us to understand that non-variable forms would not satisfy the functional equation universally.
Checking specific values and transformations, we also observe:
If we assume , substitute back:
Remarkably, operations simplify to show consistency as well:
Both forms and satisfy the functional equation. Thus, these are the functional solutions.
Therefore, the solutions are:
These solutions represent all functions that satisfy the given equation for all .