If there is a closed-form rule for a function, and the function is linear, it will be in the form y = Mx + B, where M and B can be any real number -- positive, negative, or 0. Note Problems D5 and D7, in which one of the two values is 0.
If there is a recursive rule given, it should be in the form yn = yn-1 + M, where M is the slope of the line.
If a situation is described, it should involve a constant rate of change, such as a constant speed of a car, the constant slope of a ramp, or the constant price of gasoline per gallon.
If a table is given, the rate of change (change in output, divided by change in input) should always be the same number. If inputs are a sequence of numbers (like 1, 2, 3, 4, 5), the outputs should also form a sequence (3, 5, 7, 9, 11; 5, 10, 15, 20, 25).
If a graph is given, it should be a straight line (a linear function).
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