The equation of a direct proportion is when two variables increase or decrease together at a constant rate. In other words, as one variable increases, the other variable also increases, and vice versa. A common form of an equation of a direct proportion is:
y = kx
where:
- y and x are the variables
- k is the constant of proportionality
For example, if y is directly proportional to x, doubling x will double y.
Looking at the options provided:
- y = z-2 is not an equation of a direct proportion because it does not have the form y = kx.
- y = -3x + 4 is not an equation of a direct proportion because it involves addition and subtraction, not a simple proportionality.
- y = -3z is not an equation of a direct proportion because it does not have the form y = kx.
Therefore, among the given options, the equation of a direct proportion is not present.
