if (a + b) + b = 180, then a + (b ⋅ 2) = 180

Start from the conclusion and work back up the proof. Click the arrow to show the parents.

• a + (b ⋅ 2) = 180,

  if the following are true:

  • a = b
  • a = c

  then b = c

  • (a + b) + b = a + (b ⋅ 2),

    if the following are true:

    • a = b
    • b = c

    then a = c

    • (a + b) + b = a + (b + b), (a + b) + c = a + (b + c)
    • a + (b + b) = a + (b ⋅ 2),

      if a = b, then x + a = x + b

      • b + b = b ⋅ 2, a + a = a ⋅ 2
  • (a + b) + b = 180