Parallelogram formulas
A parallelogram has two pairs of parallel sides. Opposite sides are equal and opposite angles are equal. Consecutive angles are supplementary (they add to 180 degrees).
Area = base * height = base * side * sin(angle). Perimeter = 2 * (base + side). Diagonals are found using the law of cosines: d1 = sqrt(a^2 + b^2 - 2ab*cos(angle)), d2 = sqrt(a^2 + b^2 + 2ab*cos(angle)).
A = b * h
Area from base b and perpendicular height h.
d = sqrt(a^2 + b^2 - 2ab*cos(theta))
Diagonal length via the law of cosines.