Grade 8 Functions Practice โ€” Easy

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Question 1 of 23: What is the definition of a function?

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Keep going: Read the lesson: What Is a Function? Line Grapher (y = mx + b) Function Grapher
Answer key for parents & teachers (23 questions)
  1. What is the definition of a function? โ€” A rule that assigns each input exactly one output. A function maps each element of the domain to exactly one element of the range โ€” one input, one output.
  2. Which ordered pair could be added to {(1,2),(3,4),(5,6)} without destroying the function? โ€” (7, 2). (7, 2) introduces a new x-value (7), keeping each input paired with exactly one output. The others repeat x-values already in the set.
  3. Using the vertical line test: if any vertical line crosses a graph at 2 or more points, the graph represents: โ€” Not a function. The vertical line test checks whether each x-value (vertical line) maps to more than one y-value. If so, it is not a function.
  4. Which of these is the domain of a function? โ€” The set of all allowable input values (x-values). The domain is the set of all valid inputs for a function.
  5. Which of these is the range of a function? โ€” The set of all output values (y-values). The range is the set of all values produced as outputs.
  6. Does the table x: 1,2,3,2 | y: 5,6,7,8 represent a function? โ€” No โ€” x=2 maps to both 6 and 8. x = 2 appears twice with different y-values (6 and 8), violating the one-output-per-input rule.
  7. Can two different inputs share the same output in a function? โ€” Yes โ€” multiple inputs can map to the same output. Functions allow many-to-one mappings (multiple inputs โ†’ same output). What is forbidden is one input โ†’ multiple outputs.
  8. The function f is defined by f(x) = xยฒ. What is f(โˆ’3)? โ€” 9. f(โˆ’3) = (โˆ’3)ยฒ = 9. Squaring a negative number gives a positive result.
  9. Which notation represents the output of a function f at input x = 7? โ€” f(7). Function notation f(7) means "evaluate f at x = 7." It is read "f of 7."
  10. What is the output when input 0 is used in f(x) = 5x โˆ’ 3? โ€” โˆ’3. f(0) = 5(0) โˆ’ 3 = โˆ’3.
  11. The graph of y = x (diagonal line through origin) โ€” does it represent a function? โ€” Yes โ€” each x-value maps to exactly one y-value. A straight line that is not vertical passes the vertical line test. y = x maps every x to exactly one y.
  12. Given g(x) = 4x โˆ’ 5, evaluate g(3). โ€” 7. g(3) = 4(3) โˆ’ 5 = 12 โˆ’ 5 = 7.
  13. Given h(x) = xยฒ โˆ’ 2, evaluate h(0). โ€” โˆ’2. h(0) = 0ยฒ โˆ’ 2 = โˆ’2.
  14. Given f(x) = 6, what is f(100)? โ€” 6. f(x) = 6 is a constant function โ€” every input gives output 6.
  15. Which representation gives the y-intercept most directly? โ€” Equation in slope-intercept form y = mx + b. In y = mx + b, b is the y-intercept โ€” you can read it directly from the equation.
  16. A linear function's graph is: โ€” A straight line. A linear function has a constant rate of change, and its graph is always a straight line.
  17. Which equation represents a linear function? โ€” y = 3x + 2. y = 3x + 2 is in the form y = mx + b with constant slope 3. The others are nonlinear (quadratic, exponential, cubic).
  18. Which equation represents a nonlinear function? โ€” y = xยฒ. y = xยฒ is quadratic โ€” its graph is a parabola, which curves. All others are linear.
  19. In a table, x increases by 1 each time. For a linear function, y should: โ€” Increase by the same amount each time. Linear functions have constant rate of change. For equal x-steps, y changes by the same amount each time.
  20. A table shows: x = 0, 1, 2, 3 and y = 2, 4, 6, 8. Is this linear or nonlinear? โ€” Linear โ€” y increases by 2 each time. ฮ”y = 2 consistently for every unit increase in x. Constant rate of change = linear.
  21. A table shows: x = 0, 1, 2, 3 and y = 1, 2, 4, 8. Is this linear or nonlinear? โ€” Nonlinear โ€” y doubles each time (exponential). ฮ”y: 1, 2, 4 โ€” not constant. This is exponential (y = 2หฃ), which is nonlinear.
  22. A nonlinear function's rate of change is: โ€” Varying (not constant). The defining characteristic of a nonlinear function is that its rate of change varies โ€” it is not constant between different intervals.
  23. On a graph, how can you quickly tell if a function is nonlinear? โ€” The graph is not a straight line (it curves). Any graph that is not a perfectly straight line represents a nonlinear function. Look for curves, parabolas, or exponential shapes.