Question

2+4+6+8+.........+2x=210

Answer 1

 2 + 4 + 6 + 8 + .... + 2x = 210

\(\Rightarrow\) 2.1 + 2.2 + 2.3 + 2.4 + ..... + 2x = 210

\(\Rightarrow\) 2 . ( 1 + 2 + 3 + 4 + .... + x ) = 210

\(\Rightarrow\) 2 . [ x . ( x + 1 ) : 2 ] = 210

\(\Rightarrow\) x . ( x + 1 ) = 210  hay x . ( x + 1 ) = 14 . ( 14 + 1 )

Vậy x = 14

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