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The drill
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Question 1
Guide question E4.1
If f(x) = x2 − 2x, what is f(−2)?
Enter an integer, decimal or fraction without units. Use up to 5 characters, or 6 including a leading minus.
Why this answer
8. Replace both occurrences of x with (−2): f(−2) = (−2)2 − 2(−2) = 4 + 4 = 8. The input is negative, but the output need not be. Parentheses keep the two negative signs in the product visible. Repair: Example 4.03.
If g(x) = 3x + 1, for what value of x is g(x) = 16?
Enter an integer, decimal or fraction without units. Use up to 5 characters, or 6 including a leading minus.
Why this answer
5. The given number 16 is an output. Set the rule equal to it: 3x + 1 = 16, so 3x = 15 and x = 5. Evaluating g(16) would answer a different question. Check: g(5) = 3(5) + 1 = 16. Repair: Example 4.05.
Write your complete response before opening the model answer. Compare both your answer and your reasoning.
Guide question E4.3
A linear function has values L(2) = 9, L(5) = 18, and L(9) = 30. Find its rate of change and a formula for L(x).
Show model answerHide model answer for question E4.3
Rate 3;L(x) = 3x + 3. Use two input-output pairs: (18 − 9)/(5 − 2) = 9/3 = 3. The next pair gives (30 − 18)/(9 − 5) = 12/4 = 3, confirming the same rate. With L(x) = 3x + b, the pair (2, 9) yields 9 = 6 + b, so b = 3. Repair: Example 4.07.
Guide question E4.4
What is the real domain of h(x) = ?
Show model answerHide model answer for question E4.4
[1, 4) ∪ (4, ∞). A real square root requires x − 1 ≥ 0, so x ≥ 1. The denominator also requires x − 4 ≠ 0, so x ≠ 4. Both restrictions apply simultaneously. The equivalent verbal description is “all real x ≥ 1, except 4.” Repair: Example 4.11.
Guide question E4.5
A straight graph segment joins a closed point at (−1, 4) to an open point at (3, 0). State its domain and range.
Show model answerHide model answer for question E4.5
Domain [−1, 3); range (0, 4]. Read the input values from left to right: −1 is included and 3 is excluded. Read the output values from bottom to top: 0 is excluded and 4 is included. The segment contains all intermediate values. A decreasing graph still has its range written in increasing order. Repair: Example 4.12.
After the exit check
Check whether you confused an input with an output, inferred an unstated rule, ignored an endpoint, or used a visual distance instead of an axis value. When an equation is available, verify a graph reading by substitution.
Section 4 readiness
You should move between a rule, table, graph, and context without reversing input and output. Distinguish a function from a one-to-one function: different inputs may share an output. Use a linear model only when the information supports it.