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If 2=6 3=12 4=20 5=30 6=42 then 9=?

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2=6\\ \\ 2\cdot (2+1)=6\\ \\ 3=12\\ \\ 3\cdot (3+1)\cdot 12\\ \\ 4=20\\ \\ 4\cdot (4+1)=20\\ \\ 5=30\\ \\ 5\cdot (5+1)=30\\ \\ 6\cdot (6+1)=42\\ \\ x\cdot (x+1)={ x }^( 2 )+x\\ \\ for\quad x=9\\ \\ 9\cdot (9+1)=\quad { 9 }^( 2 )+9\quad =\quad 81+9\quad =\quad 90

User Daniel Shin
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