#38
Top 50 Mistake
Confusing gradient and y-intercept
"The m-c Mixup"
The Mistake in Action
For the line $y = 5x - 3$, state the gradient and y-intercept.
Wrong: Gradient = $-3$ y-intercept = $5$
Why It Happens
Students remember that the equation has two important numbers but mix up which is which. The order in the equation ($mx$ before $c$) can be confusing.
The Fix
In $y = mx + c$:
- $m$ is the coefficient of $x$ (the number multiplied by $x$) = gradient
- $c$ is the constant (the number on its own) = y-intercept
For $y = 5x - 3$:
- Gradient = 5 (the coefficient of $x$)
- y-intercept = $-3$ (the constant)
Memory aid: "$m$ for multiplied by $x$; $c$ for constant"
Spot the Mistake
Can you identify where this student went wrong?
For $y = 5x - 3$:
Gradient = $-3$, y-intercept = $5$
Click on the line that contains the error.
Related Topics
Learn more about the underlying maths: