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a/ Ta có :
\(9^{1945}-2^{1930}=\left(9^5\right)^{389}-\left(2^{10}\right)^{193}=\left(.....9\right)-\left(.....4\right)=\left(............5\right)⋮5\)
\(\Leftrightarrowđpcm\)
\(A=\left(2+2^2\right)+2^2\left(2+2^2\right)+...+2^{98}\left(2+2^2\right)\\ A=\left(2+2^2\right)\left(1+2^2+...+2^{98}\right)=6\left(1+2^2+...+2^{98}\right)⋮6\)
A=2+22+23+24+....+2100A=2+22+23+24+....+2100
A=(2+22)+(23+24)+....+(299+2100)A=(2+22)+(23+24)+....+(299+2100)
A=1.(2+22)+22.(2+22)+....+298.
\(2+2^2+2^3+....+2^{59}+2^{60}\)
\(=\left(2+2^2\right)+\left(2^3+2^4\right)+...+\left(2^{59}+2^{60}\right)\)
\(=2\left(1+2\right)+2^3\left(1+2\right)+.....+2^{59}\left(1+2\right)\)
\(=2.3+2^3.3+....+2^{59}.3\)
\(=3\left(2+2^3+...+2^{59}\right)\)
Vì có cơ số là 3 nên \(=3\left(2+2^3+...+2^{59}\right)\)
Vậy : \(2+2^2+2^3+....+2^{59}+2^{60}\)
\(A=4+4^2+4^3+...+4^{100}\)
\(A=\left(4+\text{ }4^2\right)+\left(4^3+4^4\right)+...+\left(4^{99}+4^{100}\right)\)
\(A=\left(1+4\right).\left(4\right)+\left(1+4\right).\left(4^3\right)+...+\left(1+4\right).\left(4^{99}\right)\)
\(A=5.\left(4+4^3+4^5+...+4^{99}\right)\)
Vậy A chia hết cho 5
Các bạn nha!
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A=2+2²+2³+...+260A=2+2²+2³+...+260
⇔ A=(2+2²)+...+(259+260)A=(2+2²)+...+(259+260)
⇔ A=2.(1+2)+...+259.(1+2)A=2.(1+2)+...+259.(1+2)
⇔ A=2.3+...+259.3A=2.3+...+259.3
⇔ A=3.(2+..+259)A=3.(2+..+259)
⇒ A⋮ 3
A=2+2²+2³+...+260A=2+2²+2³+...+260
⇔ A=(2+2²+2³)+...+(258+259260)A=(2+2²+2³)+...+(258+259260)
⇔ A=2.(1+2+2²)+...+258.(1+2+2²)A=2.(1+2+2²)+...+258.(1+2+2²)
⇔ A=2.7+...+258.7A=2.7+...+258.7
⇔ A=7.(2+...+258A=7.(2+...+258
⇒ A⋮ 7
Hiện tại mình chưa tìm ra sao chia hết cho 5 nên bạn tự làm nhé cảm ơn bạn
A=2+22+23+....+299+2100
A=(2+22+23+24+25)+(26+27+28+29+210)+......+(296+297+298+299+2100)
A=(2+22+23+24+25)+25.(2+22+23+24+25)+....+295.(2+22+23+24+25)
A=62+25.62+.....+295.62
A=62.(1+25+.....+295)
A=31.2.(1+25+...+295)\(⋮\)31
Vậy A\(⋮\)31
Chúc bn học tốt
Đặt: \(A=2+2^2+2^3+...+2^{2024}\)
\(2A=2\left(2+2^2+2^3+...+2^{2024}\right)\\2A=2^2+2^3+2^4+...+2^{2025}\\ 2A-A=\left(2^2+2^3+2^4+...+2^{2025}\right)-\left(2+2^2+2^3+...+2^{2024}\right)\\A=2^{2025}-2\)
Đặt \(A=2+2^2+2^3+2^4+...+2^{2024}\)
Ta có:
\(A=2+2^2+2^3+2^4+...+2^{2024}\\ 2A=2^2+2^3+2^4+2^5+...+2^{2025}\\ 2A-A=\left(2^2+2^3+2^4+2^5+...+2^{2025}\right)-\left(2+2^2+2^3+2^4+...+2^{2024}\right)\\ A=2^{2025}-2\)Vậy...