Question

cho A = 3+3²+3³+3⁴+3⁵+......+3¹⁰

^{CMR : A chia het} cho 4 nhung khong chia het cho 5

Answer 1

A = 3+3^2 + 3^3 +.....+ 3^10

=(3+3^2)+....+ (3^9+3^10)

=3(3+1) +....+3^9(3+1)

= 3 .4 + .....+ 3^9 . 4

= 4(3 +...+3^9) chia hết cho 4

Answer 2

giup nha ! day la bai cua e mink nhung mink ban! giups dc mink k nha!

Answer 3

 chia het cho 13 nha! mink nham!

Answer 4

A = 3+3^2 + 3^3 +...+ 3^10

= (3+3^2+3^3) +...+ (3^8+3^9+3^10)

=3( 1+3+3^2)+....+3^8(1+3+3^3)

= 3. 13 +....+ 3^8 .13

= 13(3+...+3^8) chia hết cho 13