Answer:
ab<6 units
Step-by-step explanation:
One of the basic property of any triangle is that the sum of the length of any two sides of a triangle is always greater than the length of the third side.
Here we are given a triangle abc, in whicn bc=4
ac= 8-ab
If have to make some conclusion about ab.
As per the property discussed above
ab<ac+bc
ab<8-ab+4
2ab<12
ab<6
Hence the length of ab must be less than 6 units
