Question

cho S =2+2²+2³+2⁴+...+2¹⁰chứng tỏ rằng S chia hết cho 3

Answer 1

=(2+2^2)+(2^3+2^4)+...........+(2^9+2^10)

=2x(1+2)+2^3x(1+2)+...........+2^9x(1+2)

=2x3+2^3x3+............+2^9x3

=3x(2+2^3+.....+2^9)chia hết cho 3

vậy S chia hết cho 3

Answer 2

=(2+2^2)+(2^3+2^4)+...........+(2^9+2^10)
=2x(1+2)+2^3x(1+2)+...........+2^9x(1+2)
=2x3+2^3x3+............+2^9x3
=3x(2+2^3+.....+2^9)chia hết cho 3
vậy S chia hết cho 3