The cosine ratio is given in the form:
[tex]\cos\theta=\frac{adj}{hyp}[/tex]
From the triangle in the question, the different sides are labeled with respect to angle E as follows:
[tex]\begin{gathered} hyp=EF \\ opp=DF \\ adj=DE \end{gathered}[/tex]
Therefore, the cosine ratio for ∠E will be:
[tex]\cos(\angle E)=\frac{DE}{EF}[/tex]
ANSWER
[tex]\begin{equation*} \cos(\angle E)=\frac{DE}{EF} \end{equation*}[/tex]
