fatcousin
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23×47 splits into 4 sub-rectangles · same as (2x+3)(4x+7) with x=10 · runs locally
23 × 47
15 × 13
34 × 56
99 × 99
show FOIL
step 1
step 2
step 3
step 4
⊞
23×47 = (20+3)×(40+7) = 20×40 + 20×7 + 3×40 + 3×7 = 800 + 140 + 120 + 21 = 1081 · with x=10: (2x+3)(4x+7) is the same rectangle
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