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Area of parallelograms

$A = b \cdot h$ , with the height at a right angle to the base.

Watch out: the slanted side is not the height.

Area of triangles

$A = \tfrac{1}{2} b h$ .

Watch out: do not forget the ½.

Surface area

Add the areas of all faces (square units).

Watch out: covering is area; filling is volume.

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