Question

Tính

A=1/2×9+1/9×7+1/7×19+...+1/252×509

B=1/10×9+1/18×13+1/26×17+...+1/802×405

C=2/4×7-3/5×9+2/7×10-3/9×13+...+2/301×304-3/401×405

Answer 1

B = \(\frac{1}{10.9}+\frac{1}{18.13}+\frac{1}{26.17}+...+\frac{1}{802.405}\)

B = \(\frac{2}{10.18}+\frac{2}{18.26}+\frac{2}{26.34}+...+\frac{2}{802.810}\)

B = \(\frac{1}{4}.\left(\frac{1}{10}-\frac{1}{18}+\frac{1}{18}-\frac{1}{26}+\frac{1}{26}-\frac{1}{34}+...+\frac{1}{802}-\frac{1}{810}\right)\)

B = \(\frac{1}{4}.\left(\frac{1}{10}-\frac{1}{810}\right)=\frac{1}{4}.\frac{8}{81}\)

B = \(\frac{2}{81}\)

Answer 2

thank you bạn nha

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