Side ac = 4, side bc = 6, side df = 4, and side ef = 6. what side corresponds to side ab and can be used to show that δabc ≅ δdef by sss? (enter your answer using letters only)

Side DE corresponds to side AB. To prove that two triangles are similar by SSS, we have to use three pairs of corresponding sides of two triangles. In the first triangle, we are given AC and BC, so the only side left is AB. In the second triangle, we are given DF and EF, and the only side left is DE. Since AC=DF=4, BC=EF=6, DE=AB.