Tìm STN x sao cho : a ) 225 : 15 + 3 . ( 2x + 1 ) = 270 b ) 3 . ( 2x + 1 ) ^ 3 = 81

2 bình luận về “Tìm STN x sao cho : a ) 225 : 15 + 3 . ( 2x + 1 ) = 270 b ) 3 . ( 2x + 1 ) ^ 3 = 81”

1. a.

   225:15+3.(2x+1)=270

   =>15+3.(2x+1)=270

   =>3.(2x+1)=270-15

   =>3.(2x+1)=255

   =>2x+1=255:3

   =>2x+1=85

   =>2x=85-1

   =>2x=84

   =>x=42

   Vậy x=42

   b.

   3.(2x+1)^3=81

   =>(2x+1)^3=81:3

   =>(2x+1)^3=27

   =>(2x+1)^3=3^3

   =>2x+1=3

   =>2x=3-1

   =>2x=2

   =>x=1

   Vậy x=1

    

   Trả lời
2. a ) 225 : 15 + 3 . ( 2x + 1 ) = 270

   15 + 3 . ( 2x + 1 ) = 270

   3 . ( 2x + 1 ) = 270 – 15

   3. ( 2x + 1 ) = 255

   2x + 1 = 255 : 3

   2x + 1 = 85

   2x = 84

   x = 84 : 2

   x = 42

   Vậy x = 42

   b ) 3 . $( 2x + 1 )^{3}$ = 81

   $( 2x + 1 )^{3}$ = 27

   $( 2x + 1 )^{3}$ = $3^{3}$

   2x + 1 = 3

   2x = 2

   x = 1

   Vậy x = 1.

   Trả lời