Question

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

Answer 1

=> 2.( 1 + 2 + 3 + 4 + ... + x ) = 210

=> 2.{ [ x.( x + 1 ) ] : 2 } = 210

=> x.( x + 1 ) = 210 = 14.15

=> x.( x + 1 ) = 14.( 14 + 1 )

=> x = 14

Answer 2

= \(\frac{\left(2x+2\right).x}{2}=210\)

=> (x + 1 ) . x = 210

Ta có : 210= 2 . 3 . 5 .7 = ( 2 . 7 ) . ( 3 . 5) = 14 . 1 5

Vậy x = 14