To evaluate the expression $b^2 - 4b$ when $b = -5$, let's substitute $b = -5$ into the expression:

$b^2 - 4b = (-5)^2 - 4(-5)$

1. First, calculate $(-5)^2$: $(-5)^2 = 25$

2. Now, calculate $-4(-5)$: $-4(-5) = 20$

3. Add the results: $25 + 20 = 45$

So, $b^2 - 4b = 45$ when $b = -5$.

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Here are some related questions:

1. What happens to the expression if $b$ is a positive value?
2. Can you graph the quadratic expression $b^2 - 4b$?
3. What is the factorized form of the quadratic expression $b^2 - 4b$?
4. What is the vertex of the parabola represented by $b^2 - 4b$?
5. How would the result change if we added a constant to the expression?

Tip: Always simplify individual terms before adding or subtracting them for accuracy.