Let f:R+→R+ be a function satisfying the functional equation for all x,y∈R+:
f(xy+f(x))=xf(y)+2.
To find f, consider substituting specific values for x and y to gain insights into the function’s form.
### Step 1: Functional Equation Analysis
First, set y=1:
f(x⋅1+f(x))=xf(1)+2.
This simplifies to:
f(x+f(x))=xf(1)+2.(1)
### Step 2: Consider x=1
Substituting x=1 into the original equation gives:
f(y+f(1))=f(y)+2.
This implies that for any y, the function f(y+f(1)) is simply f(y)+2. This suggests a potential linear relationship.
### Step 3: Try a Simplified Form
Assume f(x)=x+c for some constant c, and test if it satisfies the condition. Substituting into the equation f(xy+f(x))=xf(y)+2:
f(xy+x+c)=x(f(y))+2.
The left side becomes:
xy+x+f(y+c)=xy+x+y+c.
The right side is:
x(y+c)+2=xy+xc+2.
Equating both sides, we derive:
xy+x+y+c=xy+xc+2.
After solving, identify c=1.
### Step 4: Verifying the Function
Thus, we propose:
f(x)=x+1.
Verify:
Substitute f(x)=x+1 back into the original equation:
f(xy+f(x))=f(xy+x+1)=xy+x+2.
And for the right-hand side:
xf(y)+2=x(y+1)+2=xy+x+2,
which confirms the equality. Therefore, the function f(x)=x+1 satisfies the equation for all x,y∈R+.
### Conclusion
The solution confirms that f(x)=x+1 is indeed the correct and unique solution satisfying the given functional equation. Thus, the function is:
f(x)=x+1.