Answer: A) Hypotenuse-Leg
This abbreviates to HL
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Explanation:
Triangle BEC is a right triangle due to the square angle marker at angle E. This is a 90 degree angle. The side opposite the 90 degree angle is always the longest side of the right triangle, aka the hypotenuse. For triangle BEC, that is side BC. Note the tickmark here.
There's a similar tickmark on side DC, which is also a hypotenuse, but for triangle DEC. The tickmarks indicate BC = DC are congruent hypotenuse lengths. That forms the "H" in "HL".
The congruent pair of legs would be the shared overlapping side EC. We can say that EC = EC due to the reflexive property. So we have the "L" of "HL"
Using BC = DC and EC = EC, we have enough information to use HL to prove triangle BEC is congruent to triangle DEC.
