Calculate area of triangles using ½ × base × height. Find area of parallelograms using base × height. Apply area formulas to complex shapes.
Triangles and parallelograms need different formulas than rectangles because of their shapes. For triangles, we use ½ × base × height because a triangle is exactly half of a rectangle. For parallelograms, we use base × height because they have the same area as a rectangle with the same base and height, even though they're slanted.
Roofs often have triangular sections. Calculating their area helps determine how many tiles are needed and the cost of roofing materials.
Garden designs often include triangular flower beds or lawn areas. Knowing their area helps plan planting and calculate material needs.
Many buildings feature triangular and parallelogram shapes. Calculating their areas is essential for construction planning and material costs.
Learn from typical errors students make and discover how to avoid them!
What students often do wrong:
1. Using all three sides instead of base and height: Trying to multiply all three triangle sides together instead of using base and perpendicular height
2. Forgetting to halve for triangle area: Using base × height for triangles instead of ½ × base × height
Correct approach: Always identify the base and perpendicular height. Remember triangles need ½ and parallelograms don't.
Memory tip: "Triangle = half a rectangle" so remember to halve the base × height result
Draw the perpendicular height line clearly - it must make a 90° angle with the base. The height is not necessarily one of the triangle's sides.
You've mastered Area of triangles and parallelograms!
Next: Learn to calculate volume of cuboids using the three-dimensional formula