Perimeter, area and dissection
Recognise the model, justify the rule and solve independently.
IKMC Grades 7-8 - Selected Topics
Explain why a shared internal edge is not part of the outside perimeter, although the area still counts the whole covered surface.
Show that triangles whose bases lie on one line and which share the opposite vertex have areas in the ratio of their bases.
Explain why cutting and rearranging pieces without overlaps or gaps keeps the area the same but may change the perimeter.
Explain why multiplying every length by $k$ multiplies the perimeter by $k$ but the area by $k^2$.