1. In a function, every input value is related to only one output value. In consequence, a straight line on a coordinate plane where the line is perpendicular to the x-axis is not a function because the only input value would be related to infinitely many outputs.
A straight line on a coordinate plane always represents a function. False
2. Every line on a coordinate plane that is not perpendicular to the x-axis represents a function. This kind of line has the form: x = constant. The equation y = 2x + 1, has not this form, therefore it is not perpendicular to the x-axis. In consequence, The equation y = 2x + 1 represents a function is True