A = 1/15 + 1/35 + 1/63 + 1/99 +........1/9999

A = 1/3x5 + 1/5x7 + 1/7x9 + .......+ 1/99x101

A = 1/2 x (1/3 - 1/5 + 1/5 - 1/7 + 1/7 - 1/9 +..... + 1/99 - 1/101)

A = 1/2 X ( 1/3 - 1/99)

A = 1/2 x ( 1/3 - 1/101)

A = 1/2 ( 98/303)

A = 49/303

49 / 303

tick cho mk nha

49/303

tick dum di

a) \(\dfrac{-5}{9}-\dfrac{4}{15}+\dfrac{2}{9}-\dfrac{11}{15}\)

\(=\left(\dfrac{-5}{9}+\dfrac{2}{9}\right)-\left(\dfrac{4}{15}+\dfrac{11}{15}\right)\)

\(=\dfrac{-3}{9}-\dfrac{15}{15}\)

\(=-\dfrac{1}{3}-1\)

\(=-\dfrac{4}{3}\)

b) \(\dfrac{-8}{13}-\dfrac{7}{16}+\dfrac{21}{13}-\dfrac{1}{6}\)

\(=\left(\dfrac{-8}{13}+\dfrac{21}{13}\right)-\dfrac{7}{16}-\dfrac{1}{6}\)

\(=\dfrac{13}{13}-\dfrac{29}{48}\)

\(=1-\dfrac{29}{48}\)

\(=\dfrac{19}{48}\)

c) \(\dfrac{-15}{25}-\dfrac{14}{21}+\dfrac{8}{5}-\dfrac{5}{3}\)

\(=\dfrac{-3}{5}-\dfrac{2}{3}+\dfrac{8}{5}-\dfrac{5}{3}\)

\(=\left(\dfrac{-3}{5}+\dfrac{8}{5}\right)-\left(\dfrac{2}{3}+\dfrac{5}{3}\right)\)

\(=\dfrac{5}{5}-\dfrac{7}{3}\)

\(=1-\dfrac{7}{3}\)

\(=-\dfrac{4}{3}\)

a: =-5/9+2/9-11/15-4/15

=-3/9-1

=-12/9=-4/3

b: =-8/13+21/13-7/16-1/6

=1-1/6-7/16

=5/6-7/16

=19/48

c: =-15/25+8/5-2/3-5/3

=-7/3+1

=-4/3

a) \(-\dfrac{5}{9}-\dfrac{4}{15}+\dfrac{2}{9}-\dfrac{11}{15}\)

\(=\left(-\dfrac{5}{9}+\dfrac{2}{9}\right)+\left(-\dfrac{4}{15}-\dfrac{11}{15}\right)\)

\(=-\dfrac{1}{3}-1=-\dfrac{4}{3}\)

b) \(-\dfrac{8}{13}-\dfrac{7}{16}+\dfrac{21}{13}-\dfrac{1}{16}\)(sửa đề)

\(=\left(-\dfrac{8}{13}+\dfrac{21}{13}\right)+\left(-\dfrac{7}{16}-\dfrac{1}{16}\right)\)

\(=1-\dfrac{1}{2}=\dfrac{1}{2}\)

c) \(-\dfrac{15}{25}-\dfrac{14}{21}+\dfrac{8}{5}-\dfrac{5}{3}\)

\(=-\dfrac{3}{5}-\dfrac{2}{3}+\dfrac{8}{5}-\dfrac{5}{3}\)

\(=\left(-\dfrac{3}{5}+\dfrac{8}{5}\right)-\left(\dfrac{2}{3}+\dfrac{5}{3}\right)\)

\(=1-\dfrac{7}{3}=\dfrac{-4}{3}\)

a: Số số hạng là 100-50+1=51 số

Tổng là (100+50)*51/2=51*75=3825

b: Số số hạng là (223-21):2+1=102(số)

Tổng là (223+21)*102/2=12444

c: Số số hạng là (72-12):4+1=16(số)

Tổng là (72+12)*16/2=672

d: Số số hạng là (124-4):6+1=21(số)

Tổng là (124+4)*21/2=1344

a) Đặt A= \(\dfrac{1}{3}+\dfrac{1}{6}+...+\dfrac{1}{36}\)

\(\dfrac{1}{2}\)A=\(\dfrac{1}{6}+\dfrac{1}{12}+...+\dfrac{1}{72}\)

\(\dfrac{1}{2}\)A=\(\dfrac{1}{2.3}+\dfrac{1}{3.4}+...+\dfrac{1}{8.9}\)

\(\dfrac{1}{2}\)A=\(\dfrac{1}{2}-\dfrac{1}{3}+\dfrac{1}{3}-\dfrac{1}{4}+...+\dfrac{1}{8}-\dfrac{1}{9}\)

\(\dfrac{1}{2}\)A=\(\dfrac{1}{2}-\dfrac{1}{9}\)

\(\dfrac{1}{2}\)A=\(\dfrac{7}{18}\)

A=\(\dfrac{7}{9}\)

A = 1/15 + 1/35 + 1/ 63 + 1/99 + ...+ 1/9999

A     = 1/(3x5) + 1/(5x7) + 1/(7x9) + 1/(9x11) + ... + 1/(99 x 101)

Ax2 = 2/(3x5) + 2/(5x7) + 2/(7x9) + 2/(9x11) + ... + 2/(99 x 101)

Ax2 = 1/3 – 1/5 + 1/5 – 1/7 + 1/7 – 1/9 + 1/9 – 1/11 + ...+ 1/99 – 1/101

Ax2 = 1/3 – 1/101 = 98/303

A    =  98/303 : 2

A    =  49/303

tớ không chắc nhé 

ta có : (ghi lại đề)

=6+12+18+24+30/3+6+9+12+15

=2*(3/3+6/6+9/9+12/12+15/15)

=2*(1+1+1+1+1)

=2*5=10

chúc main học tốt nhé

hi

giải hộ mình với cảm ơn

Bài 2: 

a: 

=>-2x=-6

hay x=3

bài 1

a) 196:4-12.(-5)=49-(-60)=109

b)-37.(1-382)-(382.37)= -37.(-381)-14134=14097-14134=-37

\(a,12.\dfrac{-7}{11}.\dfrac{5}{6}.\dfrac{22}{7}=\left(12.\dfrac{5}{6}\right)\left(\dfrac{-7}{11}.\dfrac{22}{7}\right)=10.\left(-2\right)=-20\\ b,\dfrac{-8}{15}.\dfrac{7}{9}.\dfrac{5}{8}.\left(-18\right)=\left(\dfrac{-8}{15}.\dfrac{5}{8}\right)\left[\dfrac{7}{9}.\left(-18\right)\right]=\dfrac{-1}{3}.\left(-14\right)=\dfrac{14}{3}\)

a) 12.−711.56.227= (12.56)(−711.227)= 10.(−2)= −20.

b) −815.79.58.(−18)= (−815.58)[79.(−18)]= −13.(−14)= 143.