Learning goals: Teacher Facing Generalize (orally and in writing) that subtracting a number results in the same value as adding the additive inverse. Interpret a number line diagram that represents subtracting signed numbers as adding with an unknown addend. Use a number line diagram to find the difference of signed numbers, and explain (orally) the reasoning. Full lesson plan (warm-up, activities, synthesis, cool-down prompt) from 7.5 Rational Number Arithmetic, Grade 7.