Question

If two variables are directly proportional, what happens to the value of one as the value of the other increases?

Short answer

When two variables are directly proportional, if the value of one variable increases, the value of the other variable will also increase, maintaining the same proportion. Similarly, if the value of one variable decreases, the value of the other variable will also decrease, while maintaining the same proportion.

Step-by-step solution

Understanding Direct Proportionality

Direct proportionality means that when two variables are directly proportional, the ratio of their values will always remain constant. This relationship can be represented mathematically as: \(y = kx\) Here, y and x are the two directly proportional variables and k is the constant of proportionality.

Describing the relationship when one variable increases

Now, let's consider what happens if the value of one variable increases. Since the constant of proportionality (k) remains the same, the proportion between the variables must also hold. So, if the value of x increases, the value of y will also increase, keeping the same proportion. For instance, if k = 2, and you have the following relationship: \(y = 2x\) If we increase the value of x from 2 to 4, we can calculate the corresponding new value for y: \(y = 2 * 4 = 8\) So, when x increased from 2 to 4, the value of y increased from 4 to 8 (both doubled).

Conclusion

When two variables are directly proportional, if the value of one variable increases, the value of the other variable will also increase, and they will maintain the same proportion. Similarly, if the value of one variable decreases, the value of the other variable will also decrease, while maintaining the same proportion.

Key concepts

Constant of Proportionality

In mathematics, the constant of proportionality is a crucial element used to describe a direct proportional relationship between two variables. This constant is denoted by the symbol \(k\). When two variables are directly proportional, it means that the ratio of their values remains constant, and this constant ratio is what we call the constant of proportionality.

The mathematical expression for direct proportionality is \(y = kx\). In this equation:- \(y\) and \(x\) are variables.- \(k\) is the constant of proportionality.

This constant helps establish how much one variable changes in relation to the other. If you know the value of \(k\), you can always determine how one variable will change when the other one changes. For example, if \(k = 3\), then for every unit increase in \(x\), \(y\) increases by three units as well, maintaining the proportion.

Ratio

The concept of a ratio plays a significant role in understanding direct proportionality. A ratio is essentially a comparison between two quantities, often expressed as \(\frac{a}{b}\), where \(a\) and \(b\) are numbers or quantities. In the context of direct proportionality, the ratio between the two variables always remains equal to the constant of proportionality, \(k\).

For directly proportional variables, the ratio \(\frac{y}{x} = k\) implies that no matter how \(x\) and \(y\) change, this ratio stays the same.

Understanding ratios can help predict how changes in one variable affect the other in a predictable and uniform manner. For instance, if the initial ratio is \(\frac{2}{1}\), then doubling both numbers maintains the ratio \((\frac{4}{2})\), confirming that the relationship is consistent.

Mathematical Relationship

In direct proportionality, the mathematical relationship between two variables is clear, consistent, and predictable. This relationship is defined by a simple equation: \(y = kx\). Here, \(y\) and \(x\) work alongside each other so that any change in one induces a proportional change in the other.

This relationship is linear in nature, represented graphically as a straight line passing through the origin \((0, 0)\). The slope of this line is determined by the constant of proportionality, \(k\). This slope reflects how steeply one variable changes relative to the other.

For example, if \(k = 5\), then as \(x\) increases by 1 unit, \(y\) will increase by 5 units. Conversely, if \(x\) decreases, \(y\) will decrease in the same ratio, maintaining the mathematical relationship defined by their direct proportionality. Through understanding this relationship, you can predict outcomes reliably.