To solve the equation $x^2 - 10x = -4$ by completing the square, let's go through the steps and check if 25 should be added to both sides:

1. Start with the given equation: $x^2 - 10x = -4$

2. To complete the square, we need to take half of the coefficient of $x$ (which is $-10$), square it, and add that value to both sides. Half of $-10$ is $-5$, and squaring it gives: $(-5)^2 = 25$

3. Add 25 to both sides of the equation: $x^2 - 10x + 25 = -4 + 25$ Simplifying the right-hand side: $x^2 - 10x + 25 = 21$

Thus, to complete the square, you indeed need to add 25 to both sides. Therefore, the statement is True.

Would you like more details or have any questions on completing the square?

Here are five related questions:

1. How do you complete the square for a quadratic equation when the coefficient of $x^2$ isn't 1?
2. What is the next step after completing the square in solving a quadratic equation?
3. Can completing the square be used to derive the quadratic formula?
4. How is completing the square related to the vertex form of a quadratic equation?
5. What are the advantages of solving equations by completing the square compared to factoring?

Tip: Completing the square is especially useful when the quadratic equation doesn’t factor easily or when you're asked to rewrite the equation in vertex form.