To get the type of triangle mentioned we need to find the value of x first.
Sum of angles in a triangle add up to 180°, thus
2x+(3x-15)+(7x+15)=180
2x+3x-15+7x+15=180
12x=180
x=15°
thus the respective sizes will be:
2x=30°
3x-15=30°
7x+15=120°
Since the triangle has two congruent angles we conclude that the triangle is called Isosceles triangle
