Define $E(a,b,c) = a \times b^c$. What positive value of $r$ is the solution to the equation $E(r,r,3) = 625$?
So we are solving for $r$ in the equation $E(r,r,3) = 625$. Let's plug in the definition of $E$. So $E(r,r,3)$ is just $r * r^3$. That's right. So we have the equation $r \cdot r^3 = 625$. And that simplifies to $r^4 = 625$. Yep. Now we just need to find the 4th root of 625. 625 is 5^4, so the fourth root of 625 is 5. That's correct. So $r=5$.

