Question

bài 1: 

A= 5^2/1.6+5^2/6.11+......+5^2/26.31

B= 2-2/19+2/43-2/1943/3-3/19+3/43-3/1943

các bn ơi, giúp mk với, mk cần gấp

Answer 1

a: \(=5\left(\dfrac{5}{1\cdot6}+\dfrac{5}{6\cdot11}+...+\dfrac{5}{26\cdot31}\right)\)

\(=5\left(1-\dfrac{1}{6}+\dfrac{1}{6}-\dfrac{1}{11}+...+\dfrac{1}{26}-\dfrac{1}{31}\right)\)

\(=5\cdot\dfrac{30}{31}=\dfrac{150}{31}\)

b: \(=\dfrac{2\left(1-\dfrac{1}{19}+\dfrac{1}{43}-\dfrac{1}{1943}\right)}{3\left(1-\dfrac{1}{19}+\dfrac{1}{43}-\dfrac{1}{1943}\right)}=\dfrac{2}{3}\)

Answer 2

`a,1/5 A = 5/(1.6) + 5/(6.11) + ... + 5/(26.31)`

`1/5A = 1/1 - 1/6 + 1/6 - 1/11 + ... + 1/26 - 1/31`

`1/5 A=30/31`

`A = 150/31`

`B = (2. (1 - 1/19 + 1/43 - 1/1943))/(3 . (1 - 1/19 + 1/43 - 1/1943))`

`= 2/3`