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Tính:
A = \(\dfrac{7}{2}\) + \(\dfrac{7}{4}\) + \(\dfrac{7}{8}\) + \(\dfrac{7}{16}\)+...+ \(\dfrac{7}{256}\)
A = \(\dfrac{7}{2}\) + \(\dfrac{7}{4}\) + \(\dfrac{7}{8}\) + \(\dfrac{7}{16}\) +...+ \(\dfrac{7}{128}\)+ \(\dfrac{7}{256}\)
A\(\times\) 2 = 7 + \(\dfrac{7}{2}\) + \(\dfrac{7}{4}\) + \(\dfrac{7}{8}\)+ \(\dfrac{7}{16}\)+...+ \(\dfrac{7}{128}\)
A \(\times\) 2 - A = 7 - \(\dfrac{7}{256}\)
A \(\times\) (2-1) = \(\dfrac{1785}{256}\)
A = \(\dfrac{1785}{256}\)
A =\(\dfrac{7}{2}\)+\(\dfrac{7}{4}\)+\(\dfrac{7}{8}\)+...+\(\dfrac{7}{256}\)
A*2 =7+\(\dfrac{7}{2}\)+\(\dfrac{7}{4}\)+...+\(\dfrac{7}{256}\)
A*2-A=7-\(\dfrac{7}{256}\)
A=\(\dfrac{\text{1785 }}{256}\)
