a, bổ sung đề 

 \(\dfrac{29-x}{21}+1+\dfrac{27-x}{23}+1+\dfrac{25-x}{25}+1+\dfrac{23-x}{27}+1+\dfrac{21-x}{29}+1=0\)

\(\Leftrightarrow\dfrac{50-x}{21}+\dfrac{50-x}{23}+\dfrac{50-x}{25}+\dfrac{50-x}{27}+\dfrac{50-x}{29}=0\)

\(\Leftrightarrow\left(50-x\right)\left(\dfrac{1}{21}+\dfrac{1}{23}+\dfrac{1}{25}+\dfrac{1}{27}+\dfrac{1}{29}\ne0\right)=0\Leftrightarrow x=50\)

a)M=1+1/5+3(1/35+...+1/9603+3/9999)

M=1+1/5+3/2(101/505-5/505)

M=1+1/5+3/2*96

M=1+1/5+144/505

M=150/101

b)Đặt A=1/4^2+1/6^2+1/8^2+....+1/(2n)^2

A=1/2^2(1/2^2+1/3^2+1/3^2+...+1/n^2)

thay vào B ta có:

1/2^2<1/1,2(vì 1>0;0<1,2<2^2)

1/3^2<1/2,3;1/4^2<1.3,4;...1/n^2<1/(n-1)n

1/4+1/9+1/16+...+1/n<1/1,2+1/2,3+...+1/n(n-1)

B<1-1/2+1/2=1/3+...+1/n-1-1/n

B<1=1/n<1=>A<1/4

ko có chi?

TL :

Xac suất thực nghiệm xuất hiện mặt S là : \(\frac{7}{20}\)

HT

xác suất xuất hiện mặt S là

------------------------------------

tổng số lần tung đòng xu

là \(\frac{7}{20}\)

xác suất  xuất hiện mặt N là

\(\frac{9}{20}\)

\(\frac{-3}{4}\) và \(\frac{4}{-5}\)

Ta có:

\(\frac{-3}{4}=\frac{-3.5}{4.5}=\frac{-15}{20}\)

\(\frac{4}{-5}=\frac{-4}{5}=\frac{-4.4}{5.4}=\frac{-16}{20}\)

Mà \(\frac{-15}{20}>\frac{-16}{20}\) nên \(\frac{-3}{4}>\frac{4}{-5}\)

Vậy \(\frac{-3}{4}>\frac{4}{-5}\)

4/-5 lớn hơn nhé

\(\dfrac{2}{5}\) = \(\dfrac{2}{5}\) x \(\dfrac{1}{100}\) = \(\dfrac{2}{500}\) [ Rút gọn bằng \(\dfrac{1}{125}\) ]

\(1,5\) x \(\dfrac{1}{125}\) = \(\dfrac{3}{250}\)

19 NHA 

1 LỚN HƠN NHA

Dễ lắm = 4.03

cảm ơn ạ 

\(-\frac{5}{9}+\frac{4}{11}+\frac{7}{11}\)

\(=\left(\frac{4}{11}+\frac{7}{11}\right)-\frac{5}{9}\)

\(=1-\frac{5}{9}\)

\(=\frac{4}{9}\)

-5/9 + ( 4/11 + 7/11 )

=-5/9 + 1

= 4/9