Consecutive angles are supplementary (A + D = 180°). If one angle is right, then all angles are right. The diagonals of a parallelogram<span> bisect each other. Each </span>diagonal of a parallelogram separates it into two congruent triangles.<span> A square has got 4 sides of equal length and 4 right </span>angles<span> (right </span>angle<span> = 90 degrees). Since ALL the </span>angles<span> in a</span>quadrilateral add up<span> to 360 then 360 divided by 4 must be 90.</span>
