a)\(\frac{5}{9}\times x-1=\frac{8}{9}\)

\(\frac{5}{9}\times x=\frac{8}{9}+1\)

\(\frac{5}{9}\times x=\frac{17}{9}\)

\(x=\frac{17}{9}:\frac{5}{9}\)

\(x=\frac{17}{5}\)

b)\(x+x\times\frac{1}{3}:\frac{2}{9}+x:\frac{2}{7}=252\)

\(x+x\times\frac{3}{2}+x:\frac{2}{7}=252\)

\(x.1+x.\frac{3}{2}+x.\frac{7}{2}=252\)

\(x\left(1+\frac{3}{2}+\frac{7}{2}\right)=252\)

\(x\times6=252\)

\(x=252:6\)

\(x=42\)

a,5/9.x-1=8/9

5/9.x=17/9

x=17/5

b,x+x.1/3:2/9+x:2/7=252

x+x.1/3.9/2+x.7/2=252

x(1+1/3.9/2+7/2)=252

x.6=252

x=42

B = \(\frac{1}{10.9}+\frac{1}{18.13}+\frac{1}{26.17}+...+\frac{1}{802.405}\)

B = \(\frac{2}{10.18}+\frac{2}{18.26}+\frac{2}{26.34}+...+\frac{2}{802.810}\)

B = \(\frac{1}{4}.\left(\frac{1}{10}-\frac{1}{18}+\frac{1}{18}-\frac{1}{26}+\frac{1}{26}-\frac{1}{34}+...+\frac{1}{802}-\frac{1}{810}\right)\)

B = \(\frac{1}{4}.\left(\frac{1}{10}-\frac{1}{810}\right)=\frac{1}{4}.\frac{8}{81}\)

B = \(\frac{2}{81}\)

thank you bạn nha

Cô mik cũg cho bài này

\(a+a.\frac{3}{2}+a:\frac{2}{7}=252\)

=>\(a+a.\frac{3}{2}+a.\frac{7}{2}=252\)

=>\(a.\left(1+\frac{3}{2}+\frac{7}{2}\right)=252\)

=>\(a.\left(1+5\right)=252\)

=>\(a.6=252\)

=>\(a=42\)

Vậy a =42

=> a + a x 3/2 +a x 7/2 = 252

=> a x (1 + 3/2 + 7/2)   = 252

=> a x 6                        = 252

=> a                              = 252 :6 

=> a                              = 42

Vậy a = 42

a x 1 + a x3/2+a x 7/2=252

a x(1+3/2+7/2)=252

 a x 6=252 

a=252/6

a=42

Ta có : (x + 2) + (x + 5) + (x + 8) + ...... + (x + 32) = 198

<=> (x + x + x + ...... + x) + (2 + 5 + 8 + ....... + 32) = 198

<=> 11x + 187 = 198

=> 11x = 198 - 187

=> 11x = 11

=> x = 1

a . 

 \(x+x\times\frac{1}{3}\div\frac{2}{9}+x\div\frac{2}{7}=252\)

\(x+x\times\frac{3}{2}+x=252\times\frac{2}{7}\)

\(x+x\times\frac{3}{2}+x=72\)

\(x=72\div\frac{3}{2}-3x\)

\(x=48-3x\)

\(x=45\)

\(\left(x+2\right)+\left(x+5\right)+\left(x+8\right)+....\left(x+32=198\right)\)

chẳng hiểu gì 

ko hiểu thì thôi Lê Đăng Dương

a) 70.5

b) 12600

4S = 4/(5x5) + 4/(9x9) + … + 1/(409x409)

Ta thấy:

4/(5x5) < 4/(3x7) = 1/3 – 1/7

4/(9x9) < 4/(7x11) = 1/7 – 1/11

…………

4/(409x409) < 4/(407x411) = 1/407 – 1/411

Mà :

4/(3x7) + 4/(7x11) + …. + 4/(407x411) = 1/3 – 1/411 = 136/411

4S < 136/411

S < 34/411 < 34/408 = 1/12

Hay  S < 1/12

ai kết bạn không

a ) \(x+x\times\frac{1}{3}\div\frac{2}{9}+x\div\frac{2}{7}=252\)

\(x\times1+x\times\frac{1}{3}\div\frac{2}{9}+x\div\frac{2}{7}=252\)

\(x\times1+x\times\frac{1}{3}\times\frac{9}{2}+x\times\frac{7}{2}=252\)

\(x\times1+x\times\frac{9}{6}+x\times\frac{7}{2}=252\)

\(x\times\left(1+\frac{9}{6}+\frac{7}{2}\right)=252\)

\(x\times6=252\)

\(x=252\div6\)

\(x=42\)

b ) \(\left(3\times x-0,8\right)\div x+14,5=15\)

\(\left(3\times x-0,8\right)\div x=15-14,5\)

\(\left(3\times x-0,8\right)\div x=0,5\)

\(0,8\div x=3-0,5\)

\(0,8\div x=2,5\)

\(x=0,8\div2,5\)

\(x=0,32\)