So,
Remember that the cosine function is a relation between the adjacent side of the angle given and the hypotenuse of the triangle.
Then we could draw:
We're asked to find tanA, which is the relation between the opposite side of angle A and its adjacent side.
For this, we should find the value of x using the pythagorean theorem first:
[tex]\begin{gathered} x=\sqrt[]{8^2-5^2} \\ x=\sqrt[]{64-25} \\ x=\sqrt[]{39} \end{gathered}[/tex]
Now, tanA will be:
[tex]\tan A=\frac{\sqrt[]{39}}{5}[/tex]
