Question

Tính:

\(A = ​1 - 2 + 3 - 4 + ... + 97 - 98 + 99 - 100\)

\(B = \dfrac{7}{19.29} + \dfrac{7}{29.39} + \dfrac{7}{39.49} + \dfrac{7}{49.59} + \dfrac{7}{59.69} \)

Answer 1

A = 1 - 2 + 3 - 4 +...+97 - 98 + 99 - 100

A = 1 + ( -2 + 3) +...+ ( -98 + 99 ) - 100

A = 1 + 1 + ... + 1 - 100

A = 50 - 100

A = -50

B = \(\frac{7}{19.29}\) + \(\frac{7}{29.39}\) + \(\frac{7}{39.49}\) + \(\frac{7}{49.59}\) + \(\frac{7}{59.69}\)

B = 7. ( \(\frac{1}{19.29}\) + \(\frac{1}{29.39}\) + \(\frac{1}{39.49}\) + \(\frac{1}{49.59}\) + \(\frac{1}{59.69}\))

B= 7. \(\frac{1}{10}\)( \(\frac{10}{19.29}\)+ \(\frac{10}{29.39}\)+ \(\frac{10}{39.49}\)+\(\frac{10}{49.59}\)+\(\frac{10}{59.69}\))

B = 7 . \(\frac{1}{10}\) ( \(\frac{1}{19}\) - \(\frac{1}{69}\) )

B = 7 . \(\frac{1}{10}\) . \(\frac{50}{1311}\)

B = \(\frac{7}{10}\) . \(\frac{50}{1311}\)

B = \(\frac{35}{1311}\)

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