Answer:
[tex]cos(60^o)=\frac{a}{12}[/tex]
Step-by-step explanation:
The complete question in the attached figure
we know that
In the right triangle of the figure
The cosine of the angle of 60 degrees is equal to divide the adjacent side to the angle of 60 degrees (BC) by the hypotenuse (AB)
so
[tex]cos(60^o)=\frac{BC}{AB}[/tex]
we have
[tex]BC=a\ units\\AB=12\ units[/tex]
substitute the values
[tex]cos(60^o)=\frac{a}{12}[/tex]
