Question

if one angle of atriangle is equal to the some of other two show that the triangle is a right triangle

Answer 1

we know that sum of angles of a triangle is 180
a +b+c = 180
if a+b =c then
c+c = 180
2c=180
c=90
hence it is a right angled triangle

Answer 2

Let the angles be x, y, and z.
By given condition, x=y+z.
Also, x+y+z=180.
Or, x+x=180
Or, 2x=180 and x=90.
Therefore in triangle xyz, x is 90 so xyz is right angled triangle.
Hope this helped.:)