standard_description: Explain how the criteria for triangle congruence (ASA, SAS, and SSS) follow from the definition of congruence in terms of rigid motions.
problem_activity: Explain why
$${\frac{1}{2}ab\mathrm{sin}(C)}$$
gives the area of a triangle with sides
$$a$$
and
$$b$$
and included angle
$$C$$
.


aligns: no