3 2X – 9 = 3 (0,25Đ) 2X = 3 + 9 (0,25Đ) 2X = 12 (0,25Đ) X = 6 (0,25Đ) B/ A = 2+22+23+…

Bài 2: a/ 2x – 9 = 3

2

: 3

2x – 9 = 3 (0,25đ)

2x = 3 + 9 (0,25đ)

2x = 12 (0,25đ)

x = 6 (0,25đ)

b/ A = 2+2

2

+2

3

+…..+2

60

(1đ)

= (2+2

2

) + (2

3

+2

4

) + …..+( 2

59

+2

60

)

= 2(1+2) + 2

3

(1+2)+…..+2

59

(1+2)

 A chia hết cho 3

A= (2+2

2

+2

3

+2

4

) + (2

5

+2

6

+2

7

+2

8

) + ……( 2

57

+ 2

58+

2

59

+2

60

)

=2(1+2+4+8) + 2

5

( 1+2+4+8) + ……….2

57

(1+2+4+8)

 A chia hết cho 15