English I don't understand french

Okay, I understand! My apologies for using French. I will switch to English for all explanations from now on.

The $2(-1)$ comes from the formula used to find the x-coordinate of the turning point (vertex) of a quadratic function.

For a quadratic function in the standard form $f(x) = ax^2 + bx + c$:
The x-coordinate of the turning point is given by the formula:

$$x = -\frac{b}{2a}$$

In the previous question, the function was $f(x) = -x^2 + 5x - 4$.
Let's identify the coefficients $a$, $b$, and $c$ from this function:

• $a$ is the coefficient of $x^2$. Here, $a = -1$.
• $b$ is the coefficient of $x$. Here, $b = 5$.
• $c$ is the constant term. Here, $c = -4$.

Now, when we substitute these values into the formula $x = -\frac{b}{2a}$:

• We replace $b$ with 5.
• We replace $a$ with $-1$.

So, the expression becomes:

$$x = -\frac{5}{2(-1)}$$

The 2 is part of the formula itself, and the $(-1)$ is the value of $a$ from the function $f(x) = -x^2 + 5x - 4$.