= 2/2 . ( 4 / 5.7 +4 / 7.9 +...+ 4 / 59.61 )
= 4/2 . ( 2 / 5.7 +2 / 7.9 +...+ 2 / 59.61 )
= 2 . ( 7-5 / 5.7 + 9-7 / 7.9 +...+ 61-59 / 59.61 )
= 2 . ( 1/5 - 1/7 + 1/7 - 1/9 +...+ 1/59 - 1/61 )
= 2 . ( 1/5 - 1/61 )
= 2 . ( 61/305 - 5/305 )
= 2 . 56/305
= 112/305
ảnh anime đẹp thế là anime gì vậy bạn
=2(\(\frac{2}{5.7}\)+\(\frac{2}{7.9}\)+.....+\(\frac{2}{59.61}\))
=2(\(\frac{1}{5}\)-\(\frac{1}{7}\)+\(\frac{1}{7}\)-\(\frac{1}{9}\)+.......+\(\frac{1}{59}\)-\(\frac{1}{61}\))
=2(\(\frac{1}{5}\)-\(\frac{1}{61}\))
=2\(\frac{56}{305}\)
=\(\frac{112}{305}\)
Đặt \(A=\frac{4}{5.7}+\frac{4}{7.9}+......+\frac{4}{59.61}\)
\(\Rightarrow A.\frac{2}{4}=\frac{2}{5.7}+\frac{2}{7.9}+........+\frac{2}{59.61}\)
\(\Rightarrow A.\frac{2}{4}=\left(\frac{1}{5}-\frac{1}{7}\right)+\left(\frac{1}{7}-\frac{1}{9}\right)+.......+\left(\frac{1}{59}-\frac{1}{61}\right)\)
\(\Rightarrow A.\frac{2}{4}=\frac{1}{5}-\frac{1}{61}=\frac{56}{305}\)
\(\Rightarrow A=\frac{112}{305}\)
Vậy.........................
=\(4.\frac{1}{5.7+7.9+....+59.69}\)
=\(4.\frac{1}{5+69}\)
=4.\(\frac{1}{74}\)
