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\(=\dfrac{7}{19}\cdot\dfrac{5}{13}+\dfrac{7}{19}\cdot\dfrac{8}{13}-3\cdot\dfrac{7}{19}=\dfrac{7}{19}\cdot\left(\dfrac{5}{13}+\dfrac{8}{13}-3\right)=-2\cdot\dfrac{7}{19}=-\dfrac{14}{19}\)
Bài 1:
a) \(\frac{16}{15}.\frac{\left(-5\right)}{14}.\frac{54}{24}.\frac{56}{21}\)
\(=\frac{4.2.2}{5.3}.\frac{\left(-5\right)}{2.7}.\frac{3.3}{4}.\frac{8}{3}\)
\(=\frac{4.2.2.\left(-5\right).3.3.8}{5.3.2.7.4.3}\)
\(=\frac{-16}{7}\)
b) \(\frac{7}{3}.\frac{\left(-5\right)}{2}.\frac{15}{21}.\frac{4}{\left(-5\right)}\)
\(=\frac{7}{3}.\frac{\left(-5\right)}{2}.\frac{5}{7}.\frac{2.2}{\left(-5\right)}\)
\(=\frac{7.\left(-5\right).5.2.2}{3.2.7.\left(-5\right)}\)
\(=\frac{10}{3}\)
Bài 2:
a) \(\frac{21}{24}.\frac{11}{9}.\frac{5}{7}=\frac{7}{8}.\frac{11}{9}.\frac{5}{7}=\frac{11.5}{8.9}=\frac{55}{72}\)
b) \(\frac{5}{23}.\frac{17}{26}+\frac{5}{23}.\frac{9}{26}\)
\(=\frac{5}{23}.\left(\frac{17}{26}+\frac{9}{26}\right)=\frac{5}{23}.1=\frac{5}{23}\)
c) \(\left(\frac{3}{29}-\frac{1}{5}\right).\frac{29}{3}=\frac{3}{29}.\frac{29}{3}-\frac{1}{5}.\frac{29}{3}\)
\(=1-1\frac{14}{15}=\frac{14}{15}\)
Bài 3:
a) x/5 = 2/5
=> x =2
b) -4/x = 20/14 = 10/7
=> -4/x = 10/7
=> x.10 = (-4).7
x.10 = - 28
x= -28 :10
x= -2,8
c) 4/7 = 12/x = 12/ 21
=> 12/x = 12/21
=> x = 21
d) 3/7 = x / 21 = 9/21
=> x/21 = 9/21
=> x= 9
a,\(\frac{21}{25}.\frac{11}{9}.\frac{5}{7}=\frac{21.11.5}{25.9.7}=\frac{3.7.11.5}{5^2.3^2.7}=\frac{11}{5.3}=\frac{11}{15}\)
b,\(\frac{5}{23}.\frac{17}{26}+\frac{5}{23}.\frac{9}{26}=\frac{5}{23}.\left(\frac{17}{26}+\frac{9}{26}\right)=\frac{5}{23}.1=\frac{5}{23}\)
c, \(\left(\frac{3}{29}-\frac{1}{5}\right).\frac{29}{3}=\frac{3}{29}.\frac{29}{3}-\frac{1}{5}.\frac{29}{3}=1-\frac{29}{15}=-\frac{14}{15}\)
a , \(\frac{21}{25}\times\frac{11}{9}\times\frac{5}{7}\)
\(=\frac{21\times11\times5}{25\times9\times7}\)
\(=\frac{3\times7\times11\times5}{5\times5\times3\times3\times7}\)
\(=\frac{11}{5\times3}\)
\(=\frac{11}{15}\)
b , \(\frac{5}{23}\times\frac{17}{26}+\frac{5}{23}\times\frac{9}{26}\)
\(=\frac{5}{23}\times\left(\frac{17}{26}+\frac{9}{26}\right)\)
\(=\frac{5}{23}\times\frac{26}{26}\)
\(=\frac{5}{23}\times1\)
\(=\frac{5}{23}\)
c , \(\left(\frac{3}{29}-\frac{1}{5}\right)\times\frac{29}{3}\)
\(=\frac{3}{29}\times\frac{29}{3}-\frac{1}{5}\times\frac{29}{3}\)
\(=1-\frac{29}{15}\)
a)A có: (26-12)/2+1=8(số hạng)
A=(26+12)*8/2=152
b)B=1+(-2)+3+(-4)+...+2003+(-2004)+2005=(-2+1)+(-4+3)+...+(-2004+2003)+2005=(-1)+(-1)+...+(-1)+2005=(-1)*1002+2005=-1002+2005=1003
haizzz, còn lại lười làm quá
a) (- 25) x 125,4 x (-8) x (-17)
= (- 25 x 4) x (- 8 x 125) x (-17)
= (-100) x (-1000) x (-17)
= - 1 700 000
b) \(\frac{-3}{4}+\frac{2}{7}+\frac{-1}{4}+\frac{3}{5}+\frac{5}{7}\)
\(=\left(\frac{-3}{4}+\frac{-1}{4}\right)+\left(\frac{2}{7}+\frac{5}{7}\right)+\frac{3}{5}\)
\(=-1+1+\frac{3}{5}\)
\(=0+\frac{3}{5}=\frac{3}{5}\)
c) \(\frac{7}{19}.\frac{8}{11}+\frac{7}{19}.\frac{3}{11}-\frac{12}{19}\)
\(=\frac{7}{19}.\left(\frac{8}{11}+\frac{3}{11}\right)-\frac{12}{19}\)
\(=\frac{7}{19}.1-\frac{12}{19}\)
\(=\frac{7}{19}-\frac{12}{19}=\frac{-5}{19}\)
d) \(19\frac{5}{8}:\frac{7}{2013}-26\frac{5}{8}:\frac{7}{2013}\)
\(=\left(19\frac{5}{8}-26\frac{5}{8}\right):\frac{7}{2013}\)
\(=-7:\frac{7}{2013}\)
\(=-2013\)
e) \(\frac{-5}{12}.\frac{2}{11}+\frac{-5}{12}.\frac{9}{11}+\frac{5}{12}\)
\(=\frac{-5}{12}.\left(\frac{2}{11}+\frac{9}{11}\right)+\frac{5}{12}\)
\(=\frac{-5}{12}.1+\frac{5}{12}\)
\(=\frac{-5}{12}+\frac{5}{12}=0\)
~Học tốt~
A=[(1+9)+(3+7)+(5+15)+(11+13)].2
A=[10+10+20+24].2
A=64.2
A=128
B=(17+23)+(19+21)+(23+27)+(25+29)
B=40+40+50+54
B=tự tính
A=(1+9)+(3+7)+(5+15)+(7+13)+(11.2)
A=10+10+10+10+22
A=40+22
A=62
mình làm câu A thôi nhé
a. \(\left(-37\right)+14+26+37\)
\(=\left[\left(-37\right)+37\right]+\left(14+26\right)\)
\(=0+40\)
\(=40\)
b. \(\left(-24\right)+6+10+24\)
\(=\left[\left(-24\right)+24\right]+6+10\)
\(=0+6+10\)
\(=16\)
c. \(15+23+\left(-25\right)+\left(-23\right)\)
\(=\left[\left(-25\right)+15\right]+\left[\left(-23\right)+23\right]\)
\(=-10+0\)
\(=-10\)
các câu khác bn tự lm
A=\(\frac{6}{19}\). \(\frac{-7}{11}\)+\(\frac{6}{19}\).\(\frac{-4}{11}\)+\(\frac{-13}{19}\)
=\(\frac{6}{19}\).(\(\frac{-7}{11}\)+\(\frac{-4}{11}\))+\(\frac{-13}{19}\)
=\(\frac{6}{19}\).\(\frac{-11}{11}\)+\(\frac{-13}{19}\)
=\(\frac{6}{19}\).-1 +\(\frac{-13}{19}\)
=\(\frac{-6}{19}\)+\(\frac{-13}{19}\)
=\(\frac{-19}{19}\)
+1
a) A = { 13; 15; 17; ...; 29 }
=> A = { x | x là các số lẻ, x < 31 }
b) B = { 22; 24; 26; ...; 42 };
=> B = { x | x là các số chẵn, x > 44 };
c) C = { 7; 11; 15; 19; 23; 27 };
=> C = { x | x là các số lẻ, x chia 2 dư 1, x < 29 };
d) D = { 4; 9; 16; 25; 36; 49 }.
=> D = { x | x là số tự nhiên, x = n.n , x < 64}.
~ Hok T ~
Bài tập 7 Viết mỗi tập hợp sau bằng cách chỉ ra tính chất đặc trưng cho mỗi phần tử của tập hợp đó:
a) A = {13; 15; 17; ...; 29}
\(A=\left\{x\in N|\right\}13\le x< 30\) và x là số lẻ
b) B = {22; 24; 26; ...; 42}
\(B=\left\{x\in N\right\}21< x< 43\)và x là số chẵn
c) C = {7; 11; 15; 19; 23; 27}
\(C=\left\{x=4k-1,k\inℕ^∗,3< x\le31\right\}\)
d) D = {4; 9; 16; 25; 36; 49}.
\(D=\left\{x\in N|;x^2;x< 50\right\}\)
a: \(\dfrac{21}{25}\cdot\dfrac{11}{9}\cdot\dfrac{5}{7}=\dfrac{21}{7}\cdot\dfrac{5}{25}\cdot\dfrac{11}{9}\)
\(=3\cdot\dfrac{11}{9}\cdot\dfrac{1}{5}=\dfrac{11}{3}\cdot\dfrac{1}{5}=\dfrac{11}{15}\)
b: \(\dfrac{5}{23}\cdot\dfrac{17}{26}+\dfrac{5}{23}\cdot\dfrac{9}{26}\)
\(=\dfrac{5}{23}\left(\dfrac{17}{26}+\dfrac{9}{26}\right)\)
\(=\dfrac{5}{23}\cdot1=\dfrac{5}{23}\)
c: \(\dfrac{7}{13}\cdot\dfrac{5}{19}+\dfrac{7}{19}\cdot\dfrac{8}{13}-3\dfrac{7}{19}\)
\(=\dfrac{7}{19}\left(\dfrac{5}{13}+\dfrac{8}{13}\right)-3-\dfrac{7}{19}\)
\(=\dfrac{7}{19}-3-\dfrac{7}{19}=-3\)
\(a,\dfrac{21}{25}.\dfrac{11}{9}.\dfrac{5}{7}\)
\(=\dfrac{21.11.5}{25.9.7}\)
\(=\dfrac{1.11.1}{5.3.1}\)
\(=\dfrac{11}{15}\)
\(b,\dfrac{5}{23}.\dfrac{17}{26}+\dfrac{5}{23}.\dfrac{9}{26}\)
\(=\dfrac{5}{23}.\left(\dfrac{17}{26}+\dfrac{9}{26}\right)\)
\(=\dfrac{5}{23}.1\)
\(=\dfrac{5}{23}\)
\(c,\dfrac{7}{13}.\dfrac{5}{19}+\dfrac{7}{19}.\dfrac{8}{13}\)
\(=\dfrac{7}{19}.\dfrac{5}{13}+\dfrac{7}{19}.\dfrac{8}{13}\)
\(=\dfrac{7}{19}.\left(\dfrac{5}{13}+\dfrac{8}{13}\right)\)
\(=\dfrac{7}{19}.1\)
\(=\dfrac{7}{19}\)