⇒ Sim of all the three interior angles of a triangle is 180°,Meaning
: In the triangle in the picture we have three angle and given is two known angle and 1 unknown angle angle 1.
Note this is a right-angled triangle since it is also shown by the sign of of angle 90°
54°+90°+ ∠1=180°
144°+∠1=180°
∠1=180°-144°
∠1=36°
From the calculation ∠1 is equal to 36°