Question

chứng minh A = 1/5 + 1/25 + 1/44 + 1/61+ 1/85 + 1/97 < 1/2

 

Answer 1

ta có : A = 1/5 + ( 1/14+1/28+1/44)+(1/61+1/85+1/97)

A < 1/5 ( 1/14.3)+(1/61.3)

A < 1/5+ 3/14+3/61

A < 1/5 + 3/12+1/20

A < 1/5+1/4+1/20

A < 1/2 (đpcm)

đúng ko

Answer 2

Ta có : A = 1/5 + ( 1/14+1/28+1/44)+(1/61+1/85+1/97)

                A < 1/5 ( 1/14.3)+(1/61.3)

                A < 1/5+ 3/14+3/61

                A < 1/5 + 3/12+1/20

                A < 1/5+1/4+1/20

                A < 1/2 (đpcm)