Question

[Trần Thị Liên]

Cho C =75 . ( 4²⁰⁰¹ + 4²⁰⁰⁰ + 4¹⁹⁹⁹ + ... + 4² + 4 +1 )

a)chứng minh rằng C chia hêt cho 4²⁰⁰²

b)Hỏi C chia hết cho 4²⁰⁰³ dư bao nhiêu ?

Giúp nhank với nha

Answer 1

[Mặc Chinh Vũ]

Theo bài ra, ta có: \(C=75\left(4^{2001}+4^{2000}+4^{1999}+...+4^2+4+1\right)+25\)

Đặt \(S=4^{2001}+4^{2000}+4^{1999}+...+4^2+4+1\)

\(\Rightarrow4S=4^{2002}+4^{2001}+4^{2000}+...+4^3+4^2+4\)

\(\Rightarrow4S-S=4^{2002}+4^{2001}+4^{2000}+...+4^3+4^2+4-4^{2001}-4^{2000}-4^{1999}-...4^2-4-1\)

\(\Rightarrow3S=4^{2002}-1\)

\(\Rightarrow S=\dfrac{4^{2002}-1}{3}\)

Khi đó \(C=75.\dfrac{4^{2002}-1}{3}+25=\dfrac{75}{3}.\left(4^{2002}-1\right)+25=25\left(4^{2002}-1\right)+25=25\left(4^{2002}-1+1\right)=25.4^{2002}⋮4^{2002}\)

Vậy \(C⋮4^{2002}\left(đpcm\right)\)