GUIDE深度 · Deep dive
Area and Perimeter Formulas
Perimeter is boundary length; area is coverage. Rectangle area ab and perimeter 2(a+b); triangle area base×height/2; circle circumference 2πr and area πr². First confirm whether the question asks perimeter or area.
Plane shapes
Rectangle: ab, 2(a+b).
Triangle: base×height/2.
Trapezoid: (a+b)×height/2.
Circle
Circumference 2πr.
Area πr².
Sketch the shape and label the givens before substituting; this catches perimeter-versus-area mistakes early.
FAQ
Why divide by 2 for a triangle?
Two congruent triangles form a parallelogram.
What value of π?
This deck uses 3.14.