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In geometry, a parallelogram is a quadrilateral whose opposite sides are parallel and of equal length. Consequently, its opposite angles are congruent. Rhombi, oblongs and squares are all types of parallelogram; all rectangles are also parallelograms.

## Formulas

• Area $A=bh=ab\sqrt{1-\cos^2(\theta)}$
• Diangle lengths $p=\sqrt{a^2+b^2-2ab\cos(\theta)}$ , $q=\sqrt{a^2+b^2+ 2ab\cos(\theta)}$
• Circumradius $R=\sqrt{\dfrac{a^2+b^2}{4\sin^2(\theta)}}$
• Inradius $r=\frac{ab}{a+b}\sin(\theta)$