đáp án: c

;

\(\frac{2}{3}+\frac{9}{6}=\frac{4}{6}+\frac{9}{6}=\frac{4+9}{6}=\frac{13}{6}\)

\(\frac{4}{5}+\frac{25}{15}=\frac{12}{15}+\frac{25}{15}=\frac{12+25}{15}=\frac{37}{15}\)

\(\frac{20}{10}+\frac{8}{2}=2+4=6\)

\(\frac{2}{3}+\frac{9}{6}=\frac{2}{3}+\frac{3}{2}=\frac{4+9}{6}=\frac{15}{6}=\frac{5}{2}\)

\(\frac{4}{5}+\frac{25}{16}=\frac{64+125}{80}=\frac{189}{80}\)

8 + 11 = 19

mà theo mk

1 + 4 = 5

2 + 5 = 7

3 + 6 = 9

8 + 11 = 19

1-1=0

1+3+4+5+4+8+2+9+4+6x0=0

1 - 1 = 0

1 + 3 + 4 + 5 + 4 + 8 + 2 + 9 + 4 + 6 x 0 = 0

a=1+2+3+4+5+6

a=6+4+5+6

a=10+11

a=21

t tôi tôi t lại nha bn

\(A=21\)

1+2+3+4+5+6+7+8+9=45

1 + 2+ 3 + 4 + 5 + 6 +7 + 8 +9

= (1 +9) + (2+ 8) + (3 + 7) + (4+ 6) + 5

= 10 + 10 + 10 + 10 + 5

= 10 x 4 + 5

= 40 + 5

= 45

2 + 3 + 4 + 5 + 6 + 7 + 8 + 9 + 10 = ( 2 + 8 ) + ( 3 + 7 ) + ( 4 + 6 ) + 5 + 10

                                                      = 10 + 10 + 10 + 5 +10 = 45

Tk mh nhé, mơn nhìu !!!
` HOK TỐT ~

ai trả lời nhanh kb nha

\(1+2+3+4+5+6+7+8+9=45\)\(45\)

Bằng 45

\(1\frac{3}{5}x2\frac{4}{3}+\frac{2}{5}=\frac{8}{5}x\frac{10}{3}+\frac{2}{5}=\frac{16}{3}+\frac{2}{5}=\frac{86}{15}\)