a, X:100/999 + X:100=9,8

X:(100/999+100)=9,8

X;100000/999=9,8

X=9,8x10000/999

X=98000/999

b>x.2/3+x.5/2+x=1

x.(2/3+5/2+1)=1

x.25/2=1

x=6/25 Nhớ k nha

a> x.9,99+x:100=9.8

   x.9,99+x.0,01=9,8

    x.10,09=9.8

    x=980/1009

\(VT=\dfrac{1}{1.2}+\dfrac{1}{2.3}+...+\dfrac{1}{99.100}=1-\dfrac{1}{2}+\dfrac{1}{2}-\dfrac{1}{3}+...-\dfrac{1}{100}\)

\(VP=\dfrac{1}{26}+\dfrac{1}{27}+...\dfrac{1}{50}=\dfrac{2}{26}+\dfrac{2}{28}+...\dfrac{2}{50}...\)

(VP lần lượt triển khai \(\dfrac{1}{26}=\dfrac{2}{26}-\dfrac{1}{26};\dfrac{1}{28}=\dfrac{2}{28}-\dfrac{1}{28}...\))

Tiếp tục \(\dfrac{2}{26}+\dfrac{2}{28}+...\dfrac{2}{50}...=\dfrac{1}{13}+\dfrac{1}{14}+...\dfrac{1}{25}...\)

(VP lần lượt triển khai \(\dfrac{1}{14}=\dfrac{2}{14}-\dfrac{1}{14};\dfrac{1}{16}=\dfrac{2}{16}-\dfrac{1}{16}...\))

Chuyển sang VT để đơn giản phần số đối \(-\dfrac{1}{2};\dfrac{1}{2}...\)

Cuối cùng ta sẽ được \(VT=1;VP=\dfrac{2}{2}\Rightarrow VT=VP\)

⇒Đpcm

có ai giúp tôi ko tôi đang cần gấp

\(=75.\left(34+66\right)-65.100\)

\(=75.100-65.100\)

\(=100.\left(75-65\right)\)

\(=100.10\)

\(=1000\)

bạn ơi còn mấy bài trên nữa bạn giúp mk đi cảm ơn bn

\(\frac{1}{1.2}+\frac{1}{2.3}+...+\frac{1}{49.50}\)

\(=\left(\frac{1}{1}-\frac{1}{2}\right)+...+\left(\frac{1}{49}-\frac{1}{50}\right)\)

\(=\frac{1}{1}-\frac{1}{50}\)

\(=\frac{49}{50}\)

1/1.2+1/3.4+1/5.6+...+1/49.50=1/26+1/27+...+1/50

=1/1-1/2+1/3-1/4+...+1/49-1/50

=(1/1+1/3+...+1/49)-(1/2+1/4+...+1/50)

=(1/1+1/2+1/3+...+1/49+1/50)-2(1/2+1/4+...+1/50)

=1/1+1/2+1/3+...+1/50-1-1/2-1/3-...-1/25

=1/26+1/27+...+1/50 (đpcm)

1/1.2+1/3.4+1/5.6+...+1/49.50=1/26+1/27+...+1/50

=1/1-1/2+1/3-1/4+...+1/49-1/50

=(1/1+1/3+...+1/49)-(1/2+1/4+...+1/50)

=(1/1+1/2+1/3+...+1/49+1/50)-2(1/2+1/4+...+1/50)

=1/1+1/2+1/3+...+1/50-1-1/2-1/3-...-1/25

=1/26+1/27+...+1/50 (đpcm)

Hình như sai đề rồi bạn ạ

what ....... what .......what 

1/1.2+1/3.4+1/5.6+...+1/49.50=1/26+1/27+...+1/50

=1/1-1/2+1/3-1/4+...+1/49-1/50

=(1/1+1/3+...+1/49)-(1/2+1/4+...+1/50)

=(1/1+1/2+1/3+...+1/49+1/50)-2(1/2+1/4+...+1/50)

=1/1+1/2+1/3+...+1/50-1-1/2-1/3-...-1/25

=1/26+1/27+...+1/50 (đpcm)

ỦNg hộ nhà mih lại cho !!!

1/1.2+1/3.4+1/5.6+...+1/49.50=1/26+1/27+...+1/50

=1/1-1/2+1/3-1/4+...+1/49-1/50

=(1/1+1/3+...+1/49)-(1/2+1/4+...+1/50)

=(1/1+1/2+1/3+...+1/49+1/50)-2(1/2+1/4+...+1/50)

=1/1+1/2+1/3+...+1/50-1-1/2-1/3-...-1/25

=1/26+1/27+...+1/50 (đpcm)

Ung ho nha mih lai cho

\(A=\frac{1}{1.2}+\frac{1}{3.4}+\frac{1}{5.6}+...+\frac{1}{49.50}\)

=>\(A=1-\frac{1}{2}+\frac{1}{3}-\frac{1}{4}+\frac{1}{5}-\frac{1}{6}+...+\frac{1}{49}-\frac{1}{50}\)

=>\(A=1-\frac{1}{50}=\frac{49}{50}\)

mà A=49/50 

=>1/26+1/27+...+1/50 =49/50

49/50 ban oi