Answer:
B
Step-by-step explanation:
Using Pythagoras' identity in the right triangle.
The square on the hypotenuse is equal to the sum of the squares on the other 2 sides, that is
EF² + DF² = DE² , that is
EF² + 7² = 13²
EF² + 49 = 169 ( subtract 49 from both sides )
EF² = 120 ( take the square root of both sides )
EF = [tex]\sqrt{120}[/tex] → B
