C = 1 10 + 1 11 + 1 12 + ... + 1 99 + 1 100 > 1 ⇔ C = 1 10 + 1 11 + 1 12 + ... + 1 20 + 1 21 + 1 22 + ... + 1 30 + ... + 1 91 + 1 92 + ... + 1 100 C > 1 10 + 10 20 + 10 30 + ... + 10 100 > 10 20 + 10 30 + 10 60 = 1 2 + 1 3 + 1 6 = 1

C = 1 10 + 1 11 + ... + 1 100 > 1 10 + 1 100 = ... + 1 100 ⏟ 90 s o = 1 10 + 90 100 = 1

cm: f(x)+f(x-1)=1

=>A=55

55

\(\frac{1}{4.6}+\frac{1}{6.8}+.........+\frac{1}{110.112}=\frac{1}{2}.\left(\frac{2}{4.6}+\frac{2}{6.8}+......+\frac{2}{110.112}\right)\)

\(=\frac{1}{2}.\left(\frac{1}{4}-\frac{1}{6}+\frac{1}{6}-\frac{1}{8}+....+\frac{1}{110}-\frac{1}{112}\right)\)

\(=\frac{1}{2}.\left(\frac{1}{4}-\frac{1}{112}\right)=\frac{1}{2}.\frac{27}{112}=\frac{27}{224}\)

cảm ơn bạn nhìu nha

1/4*6+1/6*8+...+1/110*112

=1/4+1/6-1/6+1/8-1/8+...+1/110-1/110+1/112

=1/4+(1/6-1/6+1/8-1/8+...+1/110-1/110+1/112)

=1/4+1/112

=29/112

Ta có: 

Do đó:

A = 1 10 + 1 11 + 1 12 + ... + 1 99 + 1 100 = 1 10 + 1 11 + 1 12 + ... + 1 90 + 1 91 + 1 92 + ... 1 99 + 1 100

Đặt A 1 = 1 10 + 1 11 + 1 12 + ... + 1 90 ;  A 2 = 1 91 + 1 92 + ... 1 99 + 1 100

Ta có  1 10 > 1 90 ;   1 11 > 1 90 ;   1 12 > 1 90 ; ... ; 1 89 > 1 90

A 1 = 1 10 + 1 11 + 1 12 + ... + 1 90 > 81 ⋅ 1 90

A 1 = 1 10 + 1 11 + 1 12 + ... + 1 90 > 81 ⋅ 1 90

Tương tự  1 91 > 1 100 ;   1 92 > 1 100 ;   ... ; 1 99 > 1 100

A 2 = 1 91 + 1 92 + ... 1 99 + 1 100 > 10 ⋅ 1 100

A 2 = 1 91 + 1 92 + ... 1 99 + 1 100 > 10 100 = 1 10

A = 1 10 + 1 11 + 1 12 + ... + 1 99 + 1 100 = A 1 + A 2 > 9 10 + 1 10

A = 1 10 + 1 11 + 1 12 + ... + 1 99 + 1 100 > 1

1

\(=\dfrac{1}{110}\times\dfrac{1}{1}\times\dfrac{1}{1}\times\dfrac{114}{1}\times\dfrac{55}{57}\\ =\dfrac{114\times55}{110\times57}\\ =\dfrac{2\times1}{2\times1}=\dfrac{2}{2}=1\)

\(\dfrac{111}{110}\times\dfrac{112}{111}\times\dfrac{113}{112}\times\dfrac{114}{113}\times\dfrac{55}{57}=\dfrac{111\times112\times113\times114}{110\times111\times112\times113}\times\dfrac{55}{57}\)

                                                   \(=\dfrac{114}{110}\times\dfrac{55}{57}=\dfrac{57}{55}\times\dfrac{55}{57}=1\)

theo bài toán đã cho ta có: 88 * (112 -110 +100 - 2) = 88 * 100 = 8800