chung to rang 1/a-1/a+1 =1/a(a+1)
chung to rang 1 phan a =1 phan a+1 + 1 phan a nhan (a+1)
chung to rang 1/a =1/a+1=1/a(a+1) voi thuoc Z , a khac 0 va -1
Chung to rang 1/a=1/a+1+1/a*(a+1) voi a thuoc so nguyen , a khac 0, a khac -1
kho..................lam............................tich,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,minh..........................troi........................ret............................wa.................ung ho minh.................hu....................hu..............hu................hat..............hat....................s
bai thi .....................kho..........................kho..............troi.................thilanh.............................ret..................wa.........................dau................wa......................tich....................ung.....................ho.....................cho............do.................lanh
cho A=1/1.2+1/3.4+1/5.6+....+1/99.100 chung to rang A>7/12
Cho A=1/3^2+1/4^2+1/5^2+...+1/50^2
Chung to rang a,A>1=4 b,A>4/9
chung to rang so A la so chinh phuong biet rang
A = 1+3+5+7+...+(2n-1) voi n € N*
cho A= 1/2+1/3+1/4+....+1/16. Chung to rang A khong la so tu nhien
Cho A=1/3^2+1/4^2+1/5^2+...+1/50^2
Chung to rang a,A>1=4 b,A>4/9
cho A =1/101+1/102+1/103+...+1/200
CHUNG TO RANG
A)A>7/12
B) A>5/8