Look at the attached image. First, we divide both sides by 7 to get m + 5 = 3. Now, we subtract 5 from both sides to get m = -2. Now, we substitute m for -2. As we can see, it checks out.
It all depends upon what other things are given If hypotenuse is not given, in cosine or reciprocals are useless. In that case only tan and cot will be equally convenient if adjacent sides are given.
