Tìm số dư của phép chia sau
\(\frac{5^{52}-1}{26}\div100\)
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a, Ta có : \(5^2A=5^{52}-5^{50}+...+5^4-5^2\)
\(\Rightarrow25A+A=5^{52}-1\)\(\Rightarrow A=\dfrac{5^{52}-1}{26}\)
b, Không thấy n :vvv
c, Ta có : \(A=24\left(5^{48}+...+1\right)\)
\(=4.6.\left(5^{48}+...+1\right)\)
\(=4.6\left(5^{48}+...\right)+24\)
\(=4.5^2\left(5^{46}.6+...\right)+24=100\left(5^{46}.6+...\right)+24\)
Vậy số dư khi chia A cho 100 là 24 .
Mọi người ơi mình làm thế này có đúng ko ạ ?
1, Nhận xét: 45 : 15 = 3
do đó khi A chia cho 15 thì thương sẽ tăng lên 3 lần
mà số dư 17 > 15 nên 17 : 15 = 1 dư 2
Vậy A chia 15 thì được thương là một số gấp 3 lần thương ban đầu và cộng thêm 1 và số dư là 2.
2, Vì số đó chia cho 26 và 24 đều dư 5 nên nếu bớt đi 5 đơn vị thì số đó chia hết cho cả 24 và 26.
Số chia hết cho 24 và 26 là 312, 624, 936....
Số cần tìm là 317, 629, 941...
Nhận thấy 941 : 24 = 39 dư 5 và 941 : 26 = 36 dư 5
mà 39 - 36 = 3
Vậy Số cần phải tìm là 941
3, Gọi số cần tìm có dạng 8ab (gạch ngang trên đầu)
Giả sử thêm vào số cần tìm 2 đơn vị thì số đó chia hết cho 3 và cho 5, đồng thời chia cho 3 dư 1 do đó số đó có tận cùng là 5 => chữ số b ban đầu là 3.
Vì số đó chia cho 3 nên tổng các chữ số 8 + a + 3 = 11 + a chia cho 3 dư 1
nên a = 2, 5, 8 (vì 13 : 3 = 4 dư 1, 16 : 3 = 5 dư 1 và 19 : 3 = 6 dư 1)
Vậy số cần phải tìm là 823, 853, 883.
Lời giải:
a. $(x-3)(y+1)=5=1.5=5.1=(-1)(-5)=(-5)(-1)$
Vì $x-3, y+1$ cũng là số nguyên nên ta có bảng sau:
b.
$A=21+5+(5^2+5^3)+(5^4+5^5)+....+(5^{98}+5^{99})$
$=26+5^2(1+5)+5^4(1+5)+....+5^{98}(1+5)$
$=2+24+(1+5)(5^2+5^4+...+5^{98}$
$=2+24+6(5^2+5^4+....+5^{98})=2+6(4+5^2+5^4+...+5^{98})$
$\Rightarrow A$ chia $6$ dư $2$.
Từ đề bài ta có được các đẳng thức sau
x=24.r1+5
x=26.r2+5
r1-r2=2=>r1=r2+2
thay vào biểu thức đầu ta được
x=24.(r2+2)+5=24r2+48+5=24r2+53
=>2r2-48=0
r2=24
x=24.24+5=581
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Bài 1:
$B=1+3+3^2+3^3+...+3^{100}$
$=1+(3+3^2)+(3^3+3^4)+...+(3^{99}+3^{100})$
$=1+3(1+3)+3^3(1+3)+...+3^{99}(1+3)$
$=1+(1+3)(3+3^3+...+3^{99})=1+4(3+3^3+....+3^{99})$
$\Rightarrow B$ chia 4 dư 1.
Bài 2:
$C=5-5^2+5^3-5^4+...+5^{2023}-5^{2024}$
$5C=5^2-5^3+5^4-5^5+...+5^{2024}-5^{2025}$
$\Rightarrow C+5C=5-5^{2025}$
$6C=5-5^{2025}$
$C=\frac{5-5^{2025}}{6}$
Đặt \(A=\frac{5^{52}-1}{26}\Rightarrow A=5^{50}-5^{48}+5^{46}-4^{44}+...+5^6-5^4+5^2-1\)
\(A=5^{48}\left(5^2-1\right)+5^{44}\left(5^2-1\right)+...+5^4\left(5^2-1\right)+24\)
\(A=5^{46}.5^2.24+5^{42}.5^2.24+...+5^2.5^2.24+24\)
\(A=100.6.\left(5^{46}+5^{42}+...+5^2\right)+24\)
\(\Rightarrow A\) chia 100 dư 24