I like this a lot … feels so uncomplicated … expanding the brackets (in this situation) just feels overkill. #UKMathsChat
This 'revaluing' approach (Hackenberg calls it 'transformation') is taught at Primary … e.g. 53−19=54−20 ... but I've never seen it applied to Secondary algebra ... but if it was, things like 20−(13−2x)=15 then become possible with number knowledge rather than brackets knowledge. Hmm?!
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Piecing together thought processes for 9th century algebra … in the absence of a) symbolic algebra and b) negative numbers:
now: simplify 14 − (10 − x)
then: simplify [14] less [10 less x]
minuend: [14]
subtrahend: [10 less x]
• goal: ...
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#UKMathsChat #iTeachMath #historyofmaths