in a triangle one angle is twice of other and their sum is the third angle .the angles are

2 answers

smallest angle --- x
one of the others --- 2x
third angle = x+2x = 3x

thus:
x + 2x + 3x = 180

carry on
assuming you're working in degrees . . .

the three angles sum to 180 degrees

A = 2B
A + B = C
A + B + C = 180

then substitute