A=100/1 x 2 + 100/2 x 3 + 100/3 x 4 +...+100/99 x 100

A/100=1/1 x 2 + 1/2 x 3 + 1/3 x 4 +...+1/99 x 100

A/100=2-1/1x2 + 3-2/2x3 + ... + 100-99/99x100

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

A/100=1-1/100

A/100=99/100

A=99/100x100=99

Vậy A=99.

Ta có:

\(\frac{100}{1.2}+\frac{100}{2.3}+\frac{100}{3.4}+...+\frac{100}{99.100}\)

\(\Rightarrow100.\left(\frac{1}{1.2}+\frac{1}{2.3}+\frac{1}{3.4}+...+\frac{1}{99.100}\right)\)

\(\Rightarrow100.\left(\frac{1}{1}-\frac{1}{2}+\frac{1}{2}-\frac{1}{3}+\frac{1}{3}-\frac{1}{4}+...+\frac{1}{99}-\frac{1}{100}\right)\)

\(\Rightarrow100.\left(\frac{1}{1}-\frac{1}{100}\right)\Leftrightarrow100.\frac{99}{100}=99\)

\(\text{Ta có :}\)

\(\frac{100}{1.2}+\frac{100}{2.3}+\frac{100}{3.4}+...+\frac{100}{99.100}\)

\(=100.\left(\frac{1}{1}-\frac{1}{2}+\frac{1}{2}-\frac{1}{3}+\frac{1}{3}-\frac{1}{4}+...+\frac{1}{99}-\frac{1}{100}\right)\)

\(100.\left(\frac{1}{1}-\frac{1}{100}\right)=100.\frac{99}{100}=99\)

100.1=100

100.2=200

100.3=300

100.4=400

100.5=500

100 x 1 = 100

100 x 2 = 200

100 x 3 = 300

100 x 4 = 400

100 x 5 = 500

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100 x 1 = 100

100 x 2 = 200

100 x 3 = 300

100 x 4 = 400

100 x 5 = 500 

100 x 6 = 600

100 x 7 = 700 

100 x 8 = 800

100 x 9 = 900

k cho mình nha các bạn và kết bạn nữa

100 x 1 = 100

100 x 2 = 200

100 x 3 = 300

100 x 4 = 400

100 x 5 = 500

100 x 6 = 600

100 x 7 = 700

100 x 8 = 800

100 x 9 = 900

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giúp mik nhé cám ơn

16

=28

b) 200 x 4 = .800.....              300 x 2 = ..600....

200 x 2 = .400.....             300 x 3 = ...900...

400 x 2 = ...800...             500 x 1 = ..500....

100 x 4 = ..400....             100 x 3 = .300.....

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ai giúp mình với

a: S=1(1+1)+2(1+2)+...+100(1+100)

=1+2+...+100+1^2+2^2+...+100^2

\(=\dfrac{100\cdot102}{2}+\dfrac{100\cdot\left(100+1\right)\cdot\left(2\cdot100+1\right)}{6}\)

\(=100\cdot51+\dfrac{100\cdot101\cdot201}{6}\)

=343450

b: \(A=1\cdot2\cdot3+2\cdot3\cdot4+...+100\cdot101\cdot102\)

=>\(4\cdot A=1\cdot2\cdot3\cdot\left(4-0\right)+2\cdot3\cdot4\left(5-1\right)+...+100\cdot101\cdot102\left(103-99\right)\)

=>4*A=100*101*102*103

=>A=25*101*102*103

A.   \(\left(x+1\right)+\left(x+2\right)+......+\left(x+100\right)=5750\)

      \(x+1+x+2+....+x+100=5750\)

      \(100x+\left(1+2+3+.......+100\right)=5750\)

      \(100x+5050=5750\)

\(100x=700\)

\(x=700:100=7\)

B.   x+(1+2+......+100) = 2000

       x + 5050 = 2000

            x = 2000 - 5050

           x= -3050

C.   ( x-1 )+(x-2)+......+( x - 100 ) = 50

 x-1+x-2+.........+x-100 = 50

100x + ( -1-2-........-100  ) = 50

100x + ( - 5050 ) = 50

100x = 50 + 5050

100 x = 5100

x = 5100 : 100

x = 51

A . \(\left(x+1\right)+\left(x+2\right)+\left(x+3\right)+...+\left(x+100\right)=5750\)

\(\left(x+x+x+...+x\right)+\left(1+2+3+...+100\right)=5750\)

\(100x+5050=5750\)

\(100x=5750-5050\)

\(100x=700\)

\(\Rightarrow x=\frac{700}{100}=7\)

B. \(x+\left(1+2+3+4+5+....+100\right)=2000\)

 \(x+\frac{\left(100+1\right).100}{2}=2000\)

\(x+5050=2000\)

\(\Rightarrow x=2000-5050=-3050\)

C. \(\left(x-1\right)+\left(x-2\right)+\left(x-3\right)+....+\left(x-100\right)=50\)

\(\left(x+x+x+...+x\right)-\left(1+2+3+...+100\right)=50\)

\(100x-5050=50\)

\(100x=5100\)

\(\Rightarrow x=\frac{5100}{100}=51\)