In order to determine if two triangles are congruent, you can use SSS (side-side-side) or SAS (side-angle-side) properties. Triangles are congruent by SSS if all three sides of one triangle are congruent to a side of the other triangle. Triangles are congruent by SAS if two sides of one triangle are congruent to two sides of the other, and the angle between those sides is also congruent to the corresponding angle of the other triangle.
Sometimes, there is not enough information provided (for example, two sides being congruent without any information about the angle between them or the congruency of the third side). In this case, the congruency of two triangles cannot be determined.
In this problem we are looking at are these two triangles congruent and if so what’s the short-cut. So I’ve given you triangle ABC. So let’s look and see what we have.
We have side AB is congruent to side EF. We have side AC is congruent to side DF and we have angle A is not congruent to anything in the other triangle. So we have a problem here, we don’t have enough information that these two triangles are congruent. So all you have to do on this problem is say, 'cannot', remember that’s one word, 'be determined'.
So that way you’ll make your English teacher happy, because you noticed that is one word and you’ll make your geometry teacher happy because you got the right answer.