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acute angle: smaller than a right angle

right angle: half a straight angle  (90º)

obtuse angle: larger than a right angle

3 sides: triangle

4 sides: quadrilateral

5 sides: pentagon

6 sides: hexagon

7 sides: heptagon

8 sides: octagon

9 sides: nonagon

10 sides: decagon

classifying by sides:

a scalene triangle has no congruent sides  (and no congruent angles)

an isosceles triangle has at least two congruent sides (and the angles opposite those sides are congruent)

an equilateral triangle has all 3 sides congruent  (and an equilateral triangle is also equiangular)

classifying by angles:

acute triangle: all angles are smaller than a right angle

right triangle: a right angle is half of a straight line (angle) and it measures 90º.  A right triangle has one right angle.

obtuse triangle: an angle that is larger than a right angle is an obtuse angle.  An obtuse triangle has one obtuse angle.

some quadrilaterals are parallelograms and some are not

parallelogram: both pair of opposite sides are parallel

rhombus: equilateral quadrilateral

rectangle: equiangular quadrilateral

square: a regular quadrilateral (equilateral and equiangular)

not parallelograms

trapezoid: one pair of opposite sides are parallel

kite: in two pair, consecutive sides are congruent