1. **State the problem:** Solve the equation $x^2 + y^2 + z^2 = 3xyz$ for real numbers $x, y, z$.
2. **Recognize the form:** This is a symmetric equation in three variables. One common approach is to check for solutions where variables are equal or zero.
3. **Try the case $x = y = z = t$:**
$$t^2 + t^2 + t^2 = 3t \, t \, t \implies 3t^2 = 3t^3$$
Simplify:
$$3t^2 = 3t^3 \implies \cancel{3}t^2 = \cancel{3}t^3 \implies t^2 = t^3$$
Divide both sides by $t^2$ (assuming $t \neq 0$):
$$\frac{t^2}{\cancel{t^2}} = \frac{t^3}{\cancel{t^2}} \implies 1 = t$$
So $t = 1$ is a solution.
4. **Check $t=0$:**
If $t=0$, then $0 = 0$ holds, so $(0,0,0)$ is also a solution.
5. **Summary of equal variables case:**
Solutions are $(0,0,0)$ and $(1,1,1)$.
6. **Try if any variable is zero, say $z=0$:**
Equation becomes:
$$x^2 + y^2 + 0 = 3xy \cdot 0 = 0$$
So:
$$x^2 + y^2 = 0$$
This implies $x=0$ and $y=0$.
So $(0,0,0)$ again.
7. **Try to find other solutions:**
Rewrite the equation as:
$$x^2 + y^2 + z^2 - 3xyz = 0$$
This is a known form related to the Markov equation. The integer solutions are well-studied.
8. **Check for solutions with one variable equal to 1:**
Let $z=1$, then:
$$x^2 + y^2 + 1 = 3xy$$
Rearranged:
$$x^2 - 3xy + y^2 + 1 = 0$$
Consider this as a quadratic in $x$:
$$x^2 - 3y x + (y^2 + 1) = 0$$
Discriminant:
$$\Delta = ( -3y)^2 - 4(y^2 + 1) = 9y^2 - 4y^2 - 4 = 5y^2 - 4$$
For real $x$, $\Delta \geq 0$:
$$5y^2 - 4 \geq 0 \implies y^2 \geq \frac{4}{5}$$
So for $|y| \geq \frac{2}{\sqrt{5}}$, real $x$ exist.
9. **Final note:**
The equation has infinite real solutions, including $(0,0,0)$, $(1,1,1)$, and others satisfying the above conditions.
**Final answer:**
$$\boxed{(0,0,0), (1,1,1), \text{and infinitely many other real triples } (x,y,z) \text{ satisfying } x^2 + y^2 + z^2 = 3xyz}$$
Solve Markov 44B7E3
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