Question

Please solve in the picture!

I know the answer is that BC is not the longest side but I need an explanation

Answer 1

Explanation:

As we know that from a theorem,

A greater angle of a triangle is opposite a greater side. Let ABC be a triangle in which angle ABC is greater than angle BCA; then side AC is also greater than side AB. For if it is not greater, then AC is either equal to AB or less.

As we have angle A =120 so it means the other 2 angles will be less than angle A , hence the opposite side to angle A is BC ,

Hence BC line is the longest line in triangle ABC

Answer 2

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