How do you write an equation using letters?

To write an equation using letters, use variables to represent unknown values and constants for known values.

In mathematics, an equation is a statement that asserts the equality of two expressions. When writing an equation using letters, we typically use variables (often represented by letters like \( x \), \( y \), or \( z \)) to stand in for unknown values. Constants, which are known values, are usually represented by numbers or specific letters.

For example, if you want to express the relationship between the total cost \( C \) of buying \( n \) items, each costing \( p \) pounds, you can write the equation as:
\[ C = n \times p \]
Here, \( C \) is the total cost, \( n \) is the number of items, and \( p \) is the price per item.

Another common example is the equation of a straight line in the form \( y = mx + c \). In this equation:
- \( y \) represents the dependent variable (the value you are trying to find).
- \( x \) is the independent variable (the value you know).
- \( m \) is the gradient (slope) of the line.
- \( c \) is the y-intercept (the point where the line crosses the y-axis).

Using letters in equations allows us to generalise mathematical relationships and solve problems more flexibly. By substituting different values for the variables, we can analyse various scenarios and find solutions to a wide range of problems.