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5 / 14 + 18 / 35 + ( 5 / 4 - 5 / 4 ) : ( 5/12)^2
= 61 / 70 + 0 : ( 5 / 12)^2
= 61 / 70 + 0
= 61 / 70
![](https://rs.olm.vn/images/avt/0.png?1311)
dễ ẹc :
5+52+53+...+559+560
=(5+54)+(52+55)+(53+56)+...+(557+560)
=5+(1+53)+52+(1+53)+...+557+(1+53)
= 126 .(5+52+...+557) chia hết cho 126
(đ.p.c.m)
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\(B=\dfrac{2^{15}\cdot5^8-2^5\cdot2^9\cdot5^9}{2^{16}\cdot5^7+2^{16}\cdot5^8}=\dfrac{2^{14}\cdot5^8\cdot\left(2-5\right)}{2^{16}\cdot5^7\left(1+5\right)}=\dfrac{1}{4}\cdot5\cdot\dfrac{-1}{2}=\dfrac{-5}{8}\)
![](https://rs.olm.vn/images/avt/0.png?1311)
\(\dfrac{3}{5}\times\dfrac{2}{7}+\dfrac{3}{5}\times\dfrac{4}{7}+\dfrac{3}{5}\)
\(=\dfrac{3}{5}\times\left(\dfrac{2}{7}+\dfrac{4}{7}+1\right)\)
\(=\dfrac{3}{5}\times1\)
\(=\dfrac{3}{5}\)
\(\dfrac{3}{5}\times\dfrac{2}{7}+\dfrac{3}{5}\times\dfrac{4}{7}+\dfrac{3}{5}\)
\(=\dfrac{3}{5}\times\left(\dfrac{2}{7}+\dfrac{4}{7}+1\right)\)
\(=\dfrac{3}{5}\times1\)
\(=\dfrac{3}{5}\).
![](https://rs.olm.vn/images/avt/0.png?1311)
\(C=\frac{5^2}{1.6}+\frac{5^2}{6.11}+...+\frac{5^2}{26.31}\)
\(=5.\left(\frac{5}{1.6}+\frac{5}{6.11}+...+\frac{5}{26.31}\right)\)
\(=5.\left(1-\frac{1}{6}+\frac{1}{6}-\frac{1}{11}+...+\frac{1}{26}-\frac{1}{31}\right)\)
\(=5.\left(1-\frac{1}{31}\right)\)
\(=5.\frac{29}{31}\)
\(=\frac{145}{31}\)
![](https://rs.olm.vn/images/avt/0.png?1311)
a)ta có S=5+52+53+...+52004 =(5+52)+(53+54)+...+(52003+52004)
S=5.(1+5)+53.(1+5)+...+52003.(1+5)
S=5.6+53.6+..+52003+6
S=6.(5+53+...+52003)
Vì 6 chia hết cho 6
=> S chia hết cho 6
b)S=5.(1+5+52)+...+598.(1+5+52)
S= 5.31+...+598.31
S=31.(5+...+598)
vì 31 chia hết cho 31
=> S chia hết cho 31
c)S=5.(1+5+52+53)+...+597.(1+5+52+53)
S=5.156+...+597.156
S= 156.(5+...+597)
vì 156 chia hết cho 156
=> S chia hết cho 156
\(S=5+5^2+5^3+...+5^{2004}\)
\(=5\left(1+5\right)+5^3\left(1+5\right)+...+5^{2003}\left(1+5\right)\)
\(=\left(1+5\right)\left(5+5^3+...+5^{2003}\right)\)
\(=6\left(5+5^3+...+5^{2003}\right)\)
Vậy S chia hết cho 6.
\(S=5\left(1+5+5^2\right)+...+5^{2002}\left(1+5+5^2\right)\)
\(=\left(1+5+5^2\right)\left(5+...+5^{2002}\right)\)
\(=31\left(5+...+5^{2002}\right)\)
Vậy S chia hết cho 31.
\(S=5\left(1+5+5^2+5^3\right)+...+5^{2001}\left(1+5+5^2+5^3\right)\)
\(=\left(1+5+5^2+5^3\right)\left(5+...+5^{2001}\right)\)
\(=156\left(5+...+5^{2001}\right)\)
Vậy S chia hết cho 156.
![](https://rs.olm.vn/images/avt/0.png?1311)
B=1/5.(1+1/5+...+\(^{\frac{1}{5^{ }}99}\))
C=1/5.(1/5+\(\frac{1}{5}^3\)+...+\(\frac{1}{5}^{99}\))
![](https://rs.olm.vn/images/avt/0.png?1311)
b: \(\Leftrightarrow\left(3x-1\right)^2=25\)
\(\Leftrightarrow3x-1\in\left\{5;-5\right\}\)
hay \(x\in\left\{2;-\dfrac{4}{3}\right\}\)
c: \(\Leftrightarrow\left(2x-5\right)^3=-81\)
\(\Leftrightarrow2x-5=-3\sqrt[3]{3}\)
hay \(x=\dfrac{5-\sqrt[3]{3}}{2}\)
\(5+5=10\)
10