Question

Tìm x

2+4+6+8+...+2x = 156

 

Answer 1

2 + 4 + 6 + ... + 2x = 156
2 + 4 + 6 + ... + 2x = 2( 1 + 2 + 3 + ....+ x ) = 2 [( x + 1 ) . x/2 ] = x ( x + 1 )
→x ( x + 1 ) = 156 = 12 . 13 vậy x = 12.

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