1. Triangles and Quadrilaterals
Grade 12 Essential Math
Geometry and Trigonometry Unit

2. Types of Triangles Triangles can be classified by their sides:
Equilateral
All 3 sides are the same length
(congruent)
Isosceles
Two sides are the same length
Scalene
All sides are different lengths

3. Types of Triangles The sum of all interior angles is 180°
Triangles can also be classified by their angles:
Acute
All angles are less than 𝟗𝟎°
Right
The largest angle is exactly 𝟗𝟎°
Obtuse
The largest angle is more than 𝟗𝟎°

4. Quadrilaterals A quadrilateral is any shape with 4 sides.
The sum of all angles is 360°
You already know some:
Square
Rectangle
There are many different types of quadrilaterals

5. Types of Quadrilaterals
(4 sides)
Trapezoid (1 pair of parallel sides)
Parallelogram
(2 pairs of parallel sides)
Opposite angles are equal
Kite
2 pairs of congruent sides
Diagonals intersect
at 90⁰
Rectangle
(4 right angles)
Rhombus
(all sides same length)
Isosceles Trapezoid
(Legs are same length)
Right
Trapezoid
(two right angles)
Square
(4 right angles, all sides same)

6. Example ‹ ‹ ABCD is a parallelogram. What is the size of angle A? ‹‹
51° ‹‹

7. Why Triangles?
Triangles are important in construction and design. (bridges, roof trusses)
Triangles are strong and do not easily deform (change shape)
Triangles are the simplest polygon (only 3 sides!)

8. Why Quadrilaterals?
Quadrilaterals are used in many construction applications (patios, rooms, furniture)
Many quadrilaterals have parallel sides and 90° angles.
Why is this important? Fit well together for strength and stability in construction.
Quadrilaterals can also be easily divided into two triangles!
The advantages of both triangles and quadrilaterals! (easy to build with and strong)