#30
Top 50 Mistake
Forgetting the ½ in triangle area
"The Missing Half"
The Mistake in Action
Find the area of a triangle with base 12cm and height 8cm.
Wrong: $A = 12 \times 8 = 96\text{cm}^2$
Why It Happens
Students remember to multiply base by height but forget the crucial ½. They're calculating the area of the rectangle the triangle fits inside.
The Fix
A triangle is half of a rectangle/parallelogram with the same base and height.
$$A = \frac{1}{2} \times b \times h = \frac{1}{2} \times 12 \times 8 = 48\text{cm}^2$$
Memory aid: Triangle has half the area of a rectangle → half × base × height
Spot the Mistake
Can you identify where this student went wrong?
Triangle: base = 12cm, height = 8cm. Find the area.
$A = 12 \times 8 = 96\text{cm}^2$
Click on the line that contains the error.
Related Topics
Learn more about the underlying maths: