1. The problem statement, all variables and given/known data The sides of a triangle are [itex]x^2+3x+3, 2x+3,x^2+2x[/itex]. Prove that the greatest angle of the triangle is 120°. 2. Relevant equations 3. The attempt at a solution The greatest angle is the one opposite to the greatest side. But how to decide which one is greatest side? Also the sides are variable.