For this case we have by definition of trigonometric relations that the cosine of an angle is given by the leg adjacent to said angle on the hypotenuse of the triangle. So:
[tex]Cos (Y) = \frac {64} {80} = \frac {32} {40} = \frac {16} {20} = \frac {8} {10} = \frac {4} {5}[/tex]
After simplifying we have to:
[tex]Cos (Y) = \frac {4} {5}[/tex]
ANswer:
[tex]Cos (Y) = \frac {4} {5}=0.8[/tex]
