a + (b ⋅ (-1)) = a - b

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

• a + (b ⋅ (-1)) = a - b,

  if a = b, then b = a

  • a - b = a + (b ⋅ (-1)), a - b = a + (b ⋅ (-1))