Tính nhanh:
a) N= \(\frac{18\times275+3\times666+9\times614\times2}{1+4+7+...+58+61+62+62\times2+62\times3+62\times4-271}\).
b) M=( 1- \(\frac{1}{3}\))x( 1- \(\frac{1}{6}\))x( 1- \(\frac{1}{10}\))x( 1- \(\frac{1}{10}\))x( 1- \(\frac{1}{15}\))x( 1- \(\frac{1}{21}\))x( 1- \(\frac{1}{28}\)).
N=( \(\frac{6}{8}\)+ 1)x( \(\frac{6}{18}\)+ 1)x( \(\frac{6}{30}\)+ 1)x...x( \(\frac{6}{10100}\)+ 1).
