Question

Cho M= 75(4²⁰¹³+4²⁰¹²+......+4³+4²+4+1)+ 25. Chứng minh M chia hết 100.

Answer 1

        M=75.(4²⁰¹³+4²⁰¹²+…..+4³+4²+1)+25

=75.4²⁰¹³+75.4²⁰¹²+……+75.4³+75.4²+75.1+25

=75.4²⁰¹³+75.4²⁰¹²+……+75.4³+75.4²+75+25

=75.4²⁰¹³+75.4²⁰¹²+……+75.4³+75.4²+100

=3.(25.4).4²⁰¹²+3.(25.4).4²⁰¹¹+…..+3.(25.4).4²+3.(25.4).4+100

=3.100.4²⁰¹²+3.100.4²⁰¹¹+…..+3.100.4²+3.100.4+100

=100.(3.4²⁰¹²+3.4²⁰¹¹+…..+3.4²+3.4+1)

Vì 100 chia het 100 nen 100.(3.4²⁰¹²+3.4²⁰¹¹+…..+3.4²+3.4+1) chia het 100

Vậy M chia het 100