A Right-angled triangle is that which has a right angle. Fig. [4].)
An Acute-angled triangle is that which has three acute angles. ([Fig. 5].)
A Parallelogram is a four-sided figure which has its opposite sides parallel. Fig. [6].)
A Rhombus is a four-sided figure which has all its sides equal, but its angles are not right angles. Fig. [7].)
A Lozenge is a square set angle-wise. Fig. [8].)
Note.—A square, an oblong, a rhombus, and a rhomboid are all species of parallelograms.
Fig. 1