My triangle solver says EF ≈ 7.5 ft.
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The law of cosines is usually used for this.
EF^2 = DE^2 +DF^2 -2*DE*DF*cos(D)
.. = 6^2 +11^2 -2*6*11*cos(40°)
.. ≈ 55.88
EF ≈ √55.88 ≈ 7.5 . . . ft
_____
The law of cosines is usually used for this.
EF^2 = DE^2 +DF^2 -2*DE*DF*cos(D)
.. = 6^2 +11^2 -2*6*11*cos(40°)
.. ≈ 55.88
EF ≈ √55.88 ≈ 7.5 . . . ft