\(\frac{1}{2}+\frac{1}{6}+\frac{1}{12}+\frac{1}{20}+...+\frac{1}{132}\)

\(=\frac{1}{1.2}+\frac{1}{2.3}+\frac{1}{3.4}+\frac{1}{4.5}+...+\frac{1}{11.12}\)

\(=\frac{1}{1}-\frac{1}{2}+\frac{1}{2}-\frac{1}{3}+\frac{1}{3}-\frac{1}{4}+...+\frac{1}{11}-\frac{1}{12}\)

\(=\frac{1}{1}-\frac{1}{12}\)

\(=\frac{11}{12}\)

\(A=\frac{1}{2}+\frac{1}{6}+\frac{1}{12}+\frac{1}{20}+...+\frac{1}{132}\)

\(A=\frac{1}{1x2}+\frac{1}{2x3}+\frac{1}{3x4}+\frac{1}{4x5}+...+\frac{1}{11x12}\)

\(A=\frac{2-1}{1x2}+\frac{3-2}{2x3}+\frac{4-3}{3x4}+\frac{5-4}{4x5}+...+\frac{12-11}{11x12}\)

\(A=1-\frac{1}{2}+\frac{1}{2}-\frac{1}{3}+\frac{1}{3}-\frac{1}{4}+...+\frac{1}{11}-\frac{1}{12}\)

\(A=1-\frac{1}{12}=\frac{11}{12}\)

Đéo hiểu

Làm gì

27,135 + \(\frac{71}{100}+\frac{542}{1000}\)

= 27,135 + 0,71 + 0,542

= 27,845 + 0,542

= 28,387

a, = 27135/1000 + 710/1000 + 542/1000 = (27135+710+542)/1000 = 28387/1000 = 28,387

28,387

(6,7 + 2, 3 +5,8):1,2

14,8 : 2 

7,4

Bạn cho mình đi

\(C1:\)

\((6,7 + 2,3 + 5,8) : 1,2\)

\(= 14,8 : 1,2\)

\(= \frac {37}{3}\)

\(C2:\)
\((6,7+2,3+5,8) : 1,2 \)

\(= 6,7:1,2 + 2,3:1,2+5,8:1,2\)

\(= \frac {67}{12} + \frac {23}{12} + \frac {29}{6}\)

\(= \frac {37}{3}\)


 

Cách 1:

( 6,7 + 2,3 + 5,8 ) : 1,2

= ( 10 + 5,8 ) : 12

= 15,8 : 12

= \(\frac{79}{5}\): \(\frac{12}{1}\)

= \(\frac{79}{5}\)x \(\frac{1}{12}\)

= \(\frac{79}{60}\)

Cách 2:

( 6,7 + 2,3 + 5,8 ) : 12

= ( \(\frac{67}{10}+\frac{23}{10}+\frac{58}{10}\)) : \(\frac{12}{1}\)

= ( \(\frac{100}{10}\)+ \(\frac{58}{10}\)) : \(\frac{12}{1}\)

= \(\frac{158}{10}\): \(\frac{12}{1}\)

= \(\frac{158}{10}\)x \(\frac{1}{12}\)

= \(\frac{158}{120}\)= \(\frac{79}{60}\)

                            Giải

số a là :

   ( 5 + 2 ) : 2 = 3,5

số x là :

    5 - 3,5 = 1,5

đáp số : a = 3,5

            x = 1,5

=>x=(5-2):2=1/2

a=1/2+2=7/2

a+x=5 suy ra a=0,x=5;   a=1,x=4;    a=3,x=2;   

mà a-x=2 suy ra ko có giá trị thỏa mãn.

Ta có: \(\frac{1}{2}+\frac{1}{-3}+\frac{1}{4}+\frac{1}{6}\)

\(=\frac{1}{2}-\frac{1}{3}+\frac{1}{6}+\frac{1}{4}\)

\(=\frac{1}{6}+\frac{1}{6}-\frac{1}{4}\)

\(=\frac{1}{3}+\frac{1}{4}=\frac{7}{12}\)