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stepladder [879]

3 years ago

9

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

1 answer:

Ira Lisetskai [31]3 years ago

8 0

$
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$
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