Show that the two triangles ABC and DEF are congruent by the
HL theorem.

Since hypotenuses and legs have the same length, then both are congruent and thus, triangles ABC and DEF are congruent.
The Hypotenuse-Leg theorem states that two right triangles are congruent if and only if their hypotenuses and any of their corresponding legs are congruent. That is to say:
[tex]\overline {AC} \cong \overline {DF}[/tex], [tex]\overline{BC} \cong \overline {EF}[/tex]
[tex]AC = DF, BC = EF[/tex]
[tex]\sqrt{AB^{2}+BC^{2}} = \sqrt{DE^{2}+EF^{2}}[/tex], [tex]BC = EF[/tex]
If we know that [tex]AB = 10[/tex], [tex]BC = 4[/tex], [tex]DE = 10[/tex] and [tex]EF = 4[/tex], then we have the following outcomes:
[tex]\sqrt{10^{2}+4^{2}} = \sqrt{10^{2}+4^{2}}[/tex]
[tex]4 = 4[/tex]
Since hypotenuses and legs have the same length, then both are congruent and thus, triangles ABC and DEF are congruent.
We kindly invite to check this question on triangles: https://brainly.com/question/21972776