In a triangle, the length of two sides added together must exceed the length of the 3rd side. So, since EF is the shortest of the two givens, we know that EF + DF must be greater than DE. So we can plug in these numbers to find the minimum.
EF + DF > DE
16 + DF > 37
DF > 21
Now, for the upper maximum, we know that the two given lengths must be greater than the length of DF. So again, we can solve for the maximum using the amounts.
DE + EF > DF
37 + 16 > DF
53 > DF
With these two in mind, we know that DF must be between 21 and 53
ANSWER: The angles opposite to the two sides of the same length are congruent. A triangle without any congruent sides or angles is called a scalene triangle.
