Step 1: Note down the given side measurements

            EXAMPLE: The side lengths are IJ =30 millimeters,

                               JK =39 millimeters, and IK = 42 millimeters. 

Step 2:  Put the sides in an order

            EXAMPLE:  IJ < JK < IK

                                 30 < 39 < 42

Step 3: Note down the opposite angle of the sides  

              IJ = \angle K            

              JK = \angle I

              IK = \angle J


Step 4: Find out the largest angle of the triangle by using the side-angle relation.

            NOTE: The sides in order from smallest to largest. Their opposite angles

              are in the same order, from smallest to largest:

            EXAMPLE: IJ < JK < IK

                                 \angle K < \angle I < \angle J

                                So, the largest angle is \angle J