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Codes:AC9M8A01. Goal: simplify a linear expression using commutative/associative grouping and check equivalence. Prepare: signed term strips.
Launch · 2 min. Ask which terms in 4x+7+2x−3 change with x, and which do not.
Model · 5 min. Regroup (4x+2x)+(7−3)=6x+4. At x=2, both forms are 16. The negative sign travels with the 3.
Guided · 6 min. Simplify 3a+9+a−5=4a+4; check a=1 gives 8 in both. Ask why a means 1a, not zero.
Practice · 6 min. D12-A/B/C use different signed expressions; a table, oral grouping or wrong-step critique all require the original and simplified forms plus substitution.
Exit · 4 min. Evaluate 2n+5+3n−1 at n=2 two ways. 5n+4=14; original 4+5+6−1=14.
Note · 2 min. If learner combines unlike terms, sort variable and constant strips. If sign error, keep the −3 on one card.
Later: Optional Day12 extra adds a context, not a new rule.