one of the triangle inequalities state that the sum of any 2 sides must be larger than the third side. More importantly, the sum of the smaller two side must be longer than the largest side. So your smaller 2 sides are 1.5 and 2......which has a sum of 3.5. Your third side is 4. So the sum of the 2 sides is NOT greater than the third side.....so these cannot be the sides of a triangle. Hope this helped.