an angle that is less than 90 degrees

An angle that measures more than 90 degrees but less than 180 degrees

An angle that measures 90 degrees

Having the same size and shape

a flat shape with many straight sides and angles

A point where two or more straight lines meet.

Numbers that are easy to compute mentally

4 sides, 4 angles

5 sided polygon

8 sided polygon

Changing the order of the addends does not change the sum.

See image

Changing the grouping of numbers will NOT change the value. For example: (7 + 4) + 8 = 7 + (4 + 8) also works with multiplication

A whole number greater than 0 that has exactly two different factors, 1 and itself.

A number that is divisible by more numbers than itself and one. It has more than itself and one as factors.