Làm đại
$\begin{array}{l}
M = \dfrac{{74}}{{131}} = 0.5648854962 = > M = 74 - 131*0.564885496 = 2.4*{10^{ - 8}} = {24.10^{ - 9}}\\
M = \dfrac{{24}}{{131}} = 0.1832061069 = > M = 24 - 131*0.183206106 = 1.14*{10^{ - 7}} = {114.10^{ - 9}}\\
M = \dfrac{{114}}{{131}} = 0.8702290076 = > M = 114 - 131*0.8702290076 = 8.3*{10^{ - 8}} = 83*{10^{ - 9}}\\
M = \dfrac{{83}}{{131}} = 0.6335877863 = > M = 83 - 131*0.633587786 = 3.4*{10^{ - 8}} = 34*{10^{ - 9}}\\
M = \dfrac{{34}}{{131}} = {\rm{0}}{\rm{.2595419847}} = > M = 34 - 131*0.259541984 = 9.6*{10^{ - 8}} = 96*{10^{ - 9}}\\
M = \dfrac{{96}}{{131}} = 0.7328244275 = > M = 96 - 131*0.732824427 = 6.3*{10^{ - 8}} = 63*{10^{ - 9}}\\
M = \dfrac{{63}}{{131}} = 0.4809160305 = > M = 63 - 131*0.480916030 = 7*{10^{ - 8}} = 70*{10^{ - 9}}\\
M = \dfrac{{70}}{{131}} = 0.534351145 = > M = 70 - 131*0.53435114 = 6.6*{10^{ - 7}} = 660*{10^{ - 9}}\\
Chu kì của M = 0.(56488549618320610687022900763358778625954198473282442748091603053435114)\\
71(chuso)
\end{array}$
=> 3 Chữ số tận cùng của chu kì là 114
