First you have to calculate value of x, as sum of all three angles of a triangle is 180°. that means
[2x] + [3x - 15] + [7x + 15] = 180, 12x - 15 + 15 = 180,
12x = 180, x = 15,
angles are, {[2*15], [(3*15) - 15], [(7*15) + 15]} = {30, 30, 120},
here two angles are equal, that means triangle is isosceles.
