Step 
<u>Find the value of MN</u>
In the right triangle MNL
Applying the Pythagorean Theorem

Solve for MN

in this problem we have

Substitute in the formula above



Step 
<u>Find the value of cos (M)</u>
we know that
In the right triangle MNL

Substitute the value of MN

therefore
<u>the answer is</u>
The value of cos(M) is 