standard_description: Derive using similarity the fact that the length of the arc intercepted by an angle is proportional to the radius, and define the radian measure of the angle as the constant of proportionality; derive the formula for the area of a sector.
problem_activity: Task
Rhianna has learned the SSS  and SAS congruence tests for triangles and she wonders if these tests might work for parallelograms.
Suppose $ABCD$ and $EFGH$ are two parallelograms all of whose corresponding sides are congruent, that is $|AB| = |EF|, |BC| = |FG|, |CD| = |GH|,$ and $|DA| = |HE|$.  Is it always true that $ABCD$ is congruent to $EFGH$?
Suppose $ABCD$ and $EFGH$ are two parallelograms with a pair of congruent corresponding sides, $|AB| = |EF|$ and $|BC| = |FG|$.  Suppose also that the included angles are congruent,
$m(\angle ABC) = m(\angle EFG)$.  Are $ABCD$ and $EFGH$ congruent?


aligns: no