Grade 8 Functions Practice โ€” Medium

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Question 1 of 36: Which graph represents 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 (36 questions)
  1. Which graph represents a function? โ€” A straight line crossing the graph once per vertical line. A straight line, vertical line test: any vertical line crosses it exactly once. A circle, sideways parabola, or ellipse would be crossed twice in some places.
  2. If f(x) = 2x + 5, what value of x gives f(x) = 13? โ€” x = 4. 2x + 5 = 13 โ†’ 2x = 8 โ†’ x = 4.
  3. A vending machine takes a dollar code and gives one snack. Is this a function? โ€” Yes โ€” each code (input) gives exactly one snack (output). Each valid input (code) maps to exactly one output (snack type). This is a real-world function.
  4. Is y = xยฒ a function? โ€” Yes โ€” each x-value produces exactly one y-value. For each x input, xยฒ gives exactly one output. (โˆ’3 and 3 give the same output 9, but that does not disqualify it as a function.)
  5. Is x = 4 (a vertical line) a function of x? โ€” No โ€” x = 4 gives infinitely many y-values for one x. A vertical line fails the vertical line test: x = 4 maps the single input x = 4 to all real y-values โ€” not a function.
  6. A student claims: "If a graph passes the horizontal line test, it is a function." Is this correct? โ€” No โ€” functions require the vertical line test. The vertical line test determines if a graph is a function. The horizontal line test determines if a function is one-to-one.
  7. Which mapping represents a function from set A = {1,2,3} to set B = {4,5,6}? โ€” 1โ†’4, 2โ†’5, 3โ†’5. Only the first mapping assigns each element of A to exactly one element of B. The others map some input to two outputs.
  8. In a function machine, input 5 โ†’ output 17 and input 3 โ†’ output 11. What rule could this be? โ€” f(x) = 3x + 2. Check f(5) = 3(5)+2 = 17 โœ“ and f(3) = 3(3)+2 = 11 โœ“. The rule is f(x) = 3x + 2.
  9. Is the relationship "each student in a class โ†’ their birthday" a function? โ€” Yes โ€” each student has exactly one birthday. Each student (input) has exactly one birthday (output). Sharing birthdays is allowed โ€” multiple inputs can share an output.
  10. A table has columns x and y. If every x-value in the table is different, is it guaranteed to be a function? โ€” Yes โ€” unique x-values ensure each input has one output. With each x appearing only once, every input maps to at most one output. This is sufficient to be a function.
  11. For f(x) = |x| (absolute value), what is f(โˆ’7)? โ€” 7. |โˆ’7| = 7. The absolute value function always returns a non-negative output.
  12. Function A: y = 5x + 2. Function B: passes through (0, 4) and (1, 7). Which has a greater slope? โ€” Function A (slope 5 > B slope 3). Function B slope = (7โˆ’4)/(1โˆ’0) = 3. Function A slope = 5. Function A has the greater slope.
  13. Function C: y = 2x โˆ’ 3. Function D table: x: 0,1,2 | y: 1,4,7. Which has the greater y-intercept? โ€” Function D (b=1 > b=โˆ’3). Function C: b = โˆ’3. Function D: at x=0, y=1 so b=1. Since 1 > โˆ’3, Function D has the greater y-intercept.
  14. f(x) = โˆ’2x + 10. For what x does f(x) = 0? โ€” x = 5. โˆ’2x + 10 = 0 โ†’ โˆ’2x = โˆ’10 โ†’ x = 5.
  15. Two functions: f(x) = x + 3 and g(x) = 2x + 1. For what value of x are they equal? โ€” x = 2. x + 3 = 2x + 1 โ†’ 2 = x. So x = 2.
  16. A table shows: x: โˆ’1, 0, 1, 2 and f(x): โˆ’1, 3, 7, 11. What is the rate of change? โ€” 4. Differences: 3โˆ’(โˆ’1) = 4, 7โˆ’3 = 4, 11โˆ’7 = 4. The constant difference is 4 per unit of x.
  17. f(x) = 3x โˆ’ 1. Which ordered pair lies on this function? โ€” (2, 5). f(2) = 3(2) โˆ’ 1 = 5. So (2, 5) lies on the graph.
  18. If f(3) = 10 and f(6) = 19, what is the rate of change (assuming linear)? โ€” 3. Rate of change = (19 โˆ’ 10)/(6 โˆ’ 3) = 9/3 = 3.
  19. Given f(x) = |2x โˆ’ 4|, what is f(1)? โ€” 2. f(1) = |2(1) โˆ’ 4| = |2 โˆ’ 4| = |โˆ’2| = 2.
  20. f(x) = 2x + 4 is represented by the table x: 0,1,2,3 | y: 4,6,8,10. What is f(10)? โ€” 24. f(10) = 2(10) + 4 = 24.
  21. Evaluate f(x) = (1/2)x โˆ’ 3 at x = โˆ’4. โ€” โˆ’5. f(โˆ’4) = (1/2)(โˆ’4) โˆ’ 3 = โˆ’2 โˆ’ 3 = โˆ’5.
  22. Which function has the greater value at x = 3: f(x) = 2x + 1 or g(x) = x + 5? โ€” f(3) = 7 = g(3) = 8, so g is greater. f(3) = 2(3)+1 = 7. g(3) = 3+5 = 8. g(3) > f(3), so g is greater at x=3.
  23. A function f is shown in a graph as a straight line passing through (0, 2) and (3, 8). What is the equation? โ€” f(x) = 2x + 2. Slope = (8โˆ’2)/(3โˆ’0) = 2. y-intercept = 2. Equation: f(x) = 2x + 2.
  24. Find the input x if f(x) = 0 for f(x) = โˆ’5x + 20. โ€” x = 4. โˆ’5x + 20 = 0 โ†’ 5x = 20 โ†’ x = 4. This is the x-intercept (zero) of the function.
  25. g(x) = 3xยฒ โˆ’ x. Evaluate g(2). โ€” 10. g(2) = 3(4) โˆ’ 2 = 12 โˆ’ 2 = 10.
  26. Which pair of functions has the same y-intercept? โ€” f(x) = 5x + 3 and g(x) = โˆ’2x + 3. Both f(x) = 5x + 3 and g(x) = โˆ’2x + 3 have b = 3. The others have different y-intercepts.
  27. What is the key feature that makes a function LINEAR? โ€” The rate of change (slope) is constant. The defining feature of a linear function is its constant rate of change (slope). Equal changes in x produce equal changes in y.
  28. Which graph feature indicates a nonlinear function? โ€” A curve (parabola or exponential). Any curve โ€” whether a parabola, S-curve, or exponential โ€” indicates a nonlinear function. Linear functions only appear as straight lines.
  29. The equation y = 4 represents which type of function? โ€” Linear โ€” a horizontal line (slope = 0). y = 4 is a horizontal line with slope 0. It is still a linear function (a special case with zero slope).
  30. Table: x = 1, 2, 3, 4 and y = 3, 5, 7, 9. What is the rate of change? โ€” 2. ฮ”y = 2 for each ฮ”x = 1. Rate of change (slope) = 2.
  31. A linear function passes through (0, 3) and (2, 9). What is its slope? โ€” 3. Slope = ฮ”y/ฮ”x = (9โˆ’3)/(2โˆ’0) = 6/2 = 3.
  32. Which of these tables represents a nonlinear function? (x increases by 1 each time) โ€” y: 1, 4, 9, 16 (ฮ”y: 3, 5, 7). y: 1, 4, 9, 16 โ€” differences are 3, 5, 7 (increasing). Not constant โ†’ nonlinear (y = xยฒ).
  33. y = โˆ’3x + 1 and y = xยฒ โˆ’ 2. Which is linear? โ€” Only y = โˆ’3x + 1. y = โˆ’3x + 1 is linear (slope = โˆ’3, y-intercept = 1). y = xยฒ โˆ’ 2 is quadratic (nonlinear).
  34. Which data set does NOT represent a linear function? โ€” (1,2), (2,4), (3,8), (4,16). (1,2),(2,4),(3,8),(4,16) โ€” y doubles each time. Differences: 2, 4, 8 (not constant). This is exponential, not linear.
  35. y = 3xยฒ + x โˆ’ 5 represents which type of function? โ€” Quadratic (nonlinear). The xยฒ term makes this a quadratic (degree 2) polynomial โ€” it is nonlinear. Its graph is a parabola.
  36. A function's table shows first differences that are constant. What does this tell you? โ€” The function is linear. Constant first differences (ฮ”y) for constant ฮ”x is the hallmark of a linear function.