Question

A = 5² /1.6+5² /6.11+.....+5² /26.31

chứng tỏ A>1

Answer 1

A= 5² ​​/1.6 + 5² /6.11 +...+ 5²​ /26.31
..

​=> A= 5.( 5/ 1.6 + 5/ 6.11 +...+ 5 /26.31)

​=> A= 5.( 1- 1/6 + 1/6 - 1/11 +...+ 1/26 - 1/31)

​=> A= 5.( 1 - 1/31 )

​=> A= 5. 30/31 = 150/31 > 1

Answer 2

=>A=5²(1/1.6+1/6.11+...+1/26.31)

=>A=25/2(2/1.6+2/6.11+...+2/26.31)

=>A=25/2(1/1-1/6+1/6-1/11+....+1/26-1/31)

=>A=25/2(1+0+0+.....+1/31)

=>A=25/2X34/31

=>A=850/62

=>A=425/31

=>A>1(425>31=>A<1)