Answer:
Angles in a triangles add up to 180°
Respectively 1 : 2 : 3 is going to be 1 x , 2 x and 3 x so,
1 x + 2 x + 3 x = 180°
⇒ Simplify
6 x = 180°
⇒ Divide by 6 on both sides to isolate x
x = 30°
Since the ratio was 1 x : 2 x : 3 x and x is 30°,
30 : 60 : 90
And since there is a 90° angle, it is a right - angled triangle