To solve the functional equation for f:R→R,
f(x)f(y)=xf(f(y−x))+xf(2x)+f(x2),
for all real x,y, we proceed as follows:
1. **Substitute y=0:**
Considering y=0, the equation becomes:
f(x)f(0)=xf(f(−x))+xf(2x)+f(x2).
Notice that if f is a constant zero function, f(x)=0 for all x, then the equation holds trivially. Hence, f(x)=0 is a solution.
2. Check for non-zero solutions:
Assume there exists x0 such that f(x0)=0. Then f(y) cannot be zero for all y. With this assumption, let's explore further.
3. **Substitute x=0:**
f(0)f(y)=0for all y.
This implies f(0)=0 or f(y)=0 for all y. Since we're considering non-zero solutions, we assume f(0)=0.
4. Substitute specific values to find a pattern:
Let's use simple substitutions to analyze behavior at specific points.
**Substitute x=1:**
f(1)f(y)=f(f(y−1))+f(2)+f(1).
This implies that if f(1) is known, we could potentially express f(y) in simpler terms.
5. Try a linear solution:
Assume f(x)=cx for some constant c. Substitute into the original equation:
(cx)(cy)=x(c(c(y−x)))+x(c(2x))+c(x2).
Simplifying,
c2xy=x(c2(y−x))+2cx2+cx2.
c2xy=c2xy−c2x2+3cx2.
Equating both sides, we get:
0=−c2x2+3cx2.
x2(c2−3c)=0.
Which implies:
c2−3c=0⇒c(c−3)=0.
Thus, c=0 or c=3, leading to the solutions:
f(x)=0orf(x)=3x.
Thus, the functions that satisfy the given functional equation are f(x)=0 and f(x)=3x for all x∈R.
f(x)=0andf(x)=3xfor all x∈R