[ 121 – 3 ( 2x – 1 ) ] . 4 mũ 5 = 4 mũ 6

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[ 121 – 3 ( 2x – 1 ) ] . 4 ^ 5 = 4 ^ 6

[ 121 – 3 ( 2x – 1 ) ] = 4^6 : 4^5

[ 121 – 3 ( 2x – 1 ) ] = 4 ^1

[ 121 – 3 ( 2x – 1 ) ] = 4 

3 ( 2x – 1 ) = 121 – 4

3 ( 2x – 1 ) = 117

2x – 1 = 117 : 3 

2x -1 = 39

  2 x = 39 + 1

  2 x = 40 

    x = 40 : 2 

    x = 20