One reason that negative numbers would not make sense for values of the variables is that the solution having a negative value is not valid. It might be that the expression represents a real word problem and a negative value will not make any sense. Hope this helps.
The answer is A that’s the answer
19? Lol........................
The highlighted part of the triangle is an angle. It is on the inside of the triangle and formed by two sides coming together.
Hope this helps! :)