S2 · Algebra · ALG.FACTOR.COMMON

Factor out common factor

Intuition

Understand first, compress later.

Algebra describes structures generally: a symbol stands for a number, while the rules remain the same.

Switch representations

Multiplication as area14 · 12 = 168

10 · 104 · 1010 · 24 · 2

The rectangle is 14 wide and 12 tall, drawn to scale: its area is the product 14 · 12. Split the two sides into 10 + 4 and 10 + 2 and 4 sub-rectangles appear; their areas add back up to 168. That is exactly what the written method computes: every partial product is a piece of area.

Formal view

You can factor out common factor when you can recognise the underlying objects, select valid rules and check each step for equivalence or logical implication.

Why does it work?

This skill sits on a prerequisite network. If a step is unstable, repair the missing prerequisite instead of merely doing more items of the same type.