1. Tính nhanh:
A= (\(1-\frac{1}{9}\))x(\(1-\frac{1}{16}\))x(\(1-\frac{1}{25}\)) ..... (\(1-\frac{1}{361}\))x(\(1-\frac{1}{400}\))
B= (\(1+\frac{1}{8}\))x(\(1+\frac{1}{15}\))x(\(1+\frac{1}{24}\)) ... (\(1+\frac{1}{440}\))x(\(1+\frac{1}{483}\))
C= \(\frac{17}{23}x\frac{7}{61}+\frac{17}{23}x\frac{28}{61}+\frac{17}{23}x\frac{26}{61}\)