Question

Tính hợp lí : \(B=\frac{4}{35}+\frac{4}{63}+\frac{4}{99}+\frac{4}{143}+\frac{4}{195}\)

Answer 1

\(B=\frac{4}{35}+\frac{4}{63}+\frac{4}{99}+\frac{4}{143}+\frac{4}{195}\)

\(B=2\cdot\left(\frac{2}{5\cdot7}+\frac{2}{7\cdot9}+\frac{2}{9\cdot11}+\frac{2}{11\cdot13}+\frac{2}{13\cdot15}\right)\)

\(B=2\cdot\left(\frac{1}{5}-\frac{1}{7}+\frac{1}{7}-\frac{1}{9}+\frac{1}{9}-\frac{1}{11}+\frac{1}{11}-\frac{1}{13}+\frac{1}{13}-\frac{1}{15}\right)\)

\(B=2\cdot\left(\frac{1}{5}-\frac{1}{15}\right)\)

\(B=2\cdot\frac{2}{15}\)

\(B=\frac{4}{15}\)

Answer 2

B = 4/35 + 4/63 + 4/99 + 4/143 + 4/195

B = 4/5.7 + 4/7.9 + 4/9.11 + 4/11.13 + 4/13.15

B = 4/2 . ( 2/5.7 + 2/7.9 + 2/9.11 + 2/11.13 + 2/13.15 )

B = 4/2 . ( 1/5 - 1/7 + 1/7 - 1/9 + 1/9 - 1/11 + 1/11 - 1/13 + 1/13 - 1/15 )

B = 4/2 . ( 1/5 - 1/15 )

B = 4/2 . 2/15

B = 4/15

Answer 3

4/15 nha !

Answer 4

B=4/15 nhe

Answer 5

B= 4 / 15

Answer 6

\(B=\frac{4}{35}+\frac{4}{63}+\frac{4}{99}+\frac{4}{143}+\frac{4}{195}\)

\(B=2x\left(\frac{2}{5x7}+\frac{2}{7x9}+\frac{2}{9x11}+\frac{2}{11x13}+\frac{2}{13x15}\right)\)

\(B=2x\left(\frac{1}{5}-\frac{1}{7}+\frac{1}{7}-\frac{1}{9}+\frac{1}{9}-\frac{1}{11}+\frac{1}{11}-\frac{1}{13}+\frac{1}{13}-\frac{1}{15}\right)\)

\(B=2x\left(\frac{1}{5}-\frac{1}{15}\right)\)

\(B=2x\frac{2}{15}\)

\(B=\frac{4}{15}\)

Answer 7

\(\frac{4}{15}\)