Please solve in the picture! I know the answer is that BC is not the longest side but I need an explanation

Case : BC is the longest side

#Remember that the total degree of triangle is 180°

#If A° = 120° so B° + C° = 180°-120°

B° + C° = 60°

#From here, you already know that even the total of both of B and C is less than 120° which is the degree of A.

#If you are gonna find the length of BC, then you need to use trigonometry which will be

BC/sinA = AB/sinB = AC/sinC

#so, from here you can know that BC will be the longest one, because bigger the value, in sin, will be smaller the value

it's both, now can you answer my most recent question?