A, CHO A,B > 0, CMR

Bài 3: a, Cho a,b > 0, CMR:

1

a

+

1

b

4

a

b

b, Cho a,b,c,d > 0

CMR:

a

d

0

+

b

c

+

d

b

+

c

a

d

b

a

d

c

a

b c