Question

Cm : A = 1/1^2+ 1/2^2 + 1/3^2+ ...... +1/99^2+1/100^2 <7/4

Answer 1

A=1/1^2+ 1/2^2+ 1/3^2+...+ 1/99^2+ 1/100^2

A=1+ 1/2^2+ 1/3^2+...+ 1/99^2+ 1/100^2

A<1+(1/2^2+1/2.3+1/3/4+...+1/98.99+1/99.100) (giữ nguyên phân số 1/2^2)

A<1+ (1/4+1/2-1/3+1/3-1/4+...+1/99-1/99+1/99-1/100)

A<1+ (1/4+1/2-1/100)

Mà 1/4+1/2-1/100 <1/4+1/2=3/4

=>A<1+3/4=7/4

Answer 2

x = 3- 1 - 1

x = 1

Vậy x =1

Answer 3

1 + 1 + x = 3

 2 + x = 3

 x = 3 - 2 

x = 1

Answer 4

x = 1 nha

~~tk ik đg âm~~