Classifying Shapes

Triangles by Angles

| Type | Angles | |------|--------| | Acute triangle | All angles less than $90°$ | | Right triangle | One angle is exactly $90°$ | | Obtuse triangle | One angle is greater than $90°$ |

Triangles by Sides

| Type | Sides | |------|-------| | Equilateral | All 3 sides equal | | Isosceles | At least 2 sides equal | | Scalene | No sides equal |

Quadrilaterals (4-sided shapes)

| Shape | Properties | |-------|-----------| | Parallelogram | 2 pairs of parallel sides | | Rectangle | Parallelogram with 4 right angles | | Rhombus | Parallelogram with 4 equal sides | | Square | Rectangle AND rhombus (4 right angles, 4 equal sides) | | Trapezoid | Exactly 1 pair of parallel sides |

Shape Relationships

• Every square is a rectangle (but not every rectangle is a square)
• Every square is a rhombus (but not every rhombus is a square)
• Every rectangle is a parallelogram
• Every rhombus is a parallelogram

Perimeter

Perimeter = distance around a shape = sum of all sides

• Rectangle: $P = 2l + 2w$
• Square: $P = 4s$

Area

Area = space inside a shape (measured in square units)

• Rectangle: $A = l \times w$
• Square: $A = s^2$

Remember: Perimeter is measured in units (cm, in). Area is measured in square units (cm², in²).