HAI CÂU KHÁC NHAU NHA

1 + (-3) + 5 + (-7) + ... + 17 + (-19)

= [1 + (-3)] + [5 + (-7)] + ... + [17 + (-19)]   (có 10 cặp)

= (-2) + (-2) + ... + (-2)

= -2 . 10 = -20

-2 + 4 + (-6) + 8 + ... + (-18) + 20

= (-2 + 4) + (-6 + 8) + ... + (-18 + 20)   (có 10 cặp)

= -2 + (-2) + ... + (-2)

= -2 . 10 = -20

\(1+\left(-3\right)+5+\left(-7\right)+...+17+\left(-19\right)=\frac{\left\{1+\left(-3\right)\right\}.\left[\left(19-1\right):2+1\right]}{2}=-10\)

\(\left(-2\right)+4+\left(-6\right)+8+...+\left(-18\right)+20=\frac{\left[\left(-2\right)+4\right].\left[\left(20-2\right):2+1\right]}{2}=10\)

a: \(=\dfrac{4}{5}+\dfrac{6}{5}\cdot\dfrac{15}{7}-\dfrac{3}{7}=\dfrac{4}{5}+\dfrac{90}{35}-\dfrac{3}{7}\)

\(=\dfrac{28}{35}+\dfrac{90}{35}-\dfrac{15}{35}=\dfrac{103}{35}\)

b: \(=\dfrac{9}{13}\left(\dfrac{5}{13}-\dfrac{6}{13}-\dfrac{20}{13}\right)=\dfrac{9}{13}\cdot\dfrac{-21}{13}=\dfrac{-189}{169}\)

a, 33.( 17- 5) - 17.( 33-5)

= 33.17 - 33.5 - 17.33 + 17.5

= ( 33.17 - 17.33) - ( 33.5 - 17.5)

= 0 - 5.( 33- 17)

= - 5. 16

= - 80

b, 12 + 3.{ 90 : [ 39 - ( 2³ - 5)²]

 = 12 + 3. { 90 : [ 39 - ( 8-5)² ]}

= 12 + 3 . { 90 : [ 39 - 3² ]}

= 12 + 3.{ 90 : (39 -9)}

= 12 + 3. { 90 : 30}

= 12 + 3 . 3

= 12 + 9

= 21

c, 307 - [ (180 .4⁰ - 160 ) : 2² + 9] : 2

= 307 - [ ( 180 - 160) : 4 + 9]:2

= 307 - [ 20:4 +9 ] :2

= 307 - [ 5 + 9] : 2

= 307 - 14 : 2

= 307 - 7

= 300 

\(\dfrac{-1}{9}.\dfrac{3}{5}+\dfrac{-1}{4}.\dfrac{-4}{5}+\dfrac{1}{9}.\dfrac{2}{5}\)

\(\text{=}\dfrac{-1}{15}+\dfrac{1}{5}+\dfrac{2}{45}\)

\(\text{=}\dfrac{8}{45}\)

Áp dụng tính chất đổi dấu và giao hoán của phép nhân phân số, ta có:

\(\dfrac{-1}{9}.\dfrac{3}{5}+\dfrac{-1}{4}.\dfrac{-4}{5}+\dfrac{1}{9}.\dfrac{2}{5}=\dfrac{1}{5}.\dfrac{-3}{9}+\dfrac{1}{5}.\dfrac{4}{4}+\dfrac{1}{5}.\dfrac{2}{9}\)

                                           \(=\dfrac{1}{5}\left(-\dfrac{3}{9}+1+\dfrac{2}{9}\right)\)

                                           \(=\dfrac{1}{5}\left(-\dfrac{3}{9}+\dfrac{9}{9}+\dfrac{2}{9}\right)\)

                                           \(=\dfrac{1}{5}.\dfrac{8}{9}\)

                                           \(=\dfrac{8}{45}\)

D

a, (\(\frac{9}{25}\) - 2.18) : (\(3\frac{4}{5}\) + 0,2)

 = (\(\frac{9}{25}\) - 36) : 4

 = \(\frac{-891}{25}\) :4

 = -8,91

                                        tạm thời làm tới đây

                                           Chúc bạn học tốt 

a) (925−2.18):(345+0,2)

 = (\(\frac{9}{25}\) - 36) : (\(\frac{19}{5}\) + 0,2)

= \(\frac{-891}{25}\) : 4

= \(\frac{-891}{100}\)

b) 518−1,456:725+4,5.45

 = \(\frac{5}{18}\) - (1,456 : \(\frac{7}{25}\)) + (4,5 . \(\frac{4}{5}\))

= \(\frac{5}{18}\) - \(\frac{26}{5}\) + \(\frac{18}{5}\)

= \(\frac{-443}{90}\) + \(\frac{18}{5}\)

= \(\frac{-119}{90}\).

a) \(\left(\frac{9}{25}-2.18\right):\left(3\frac{4}{5}+0,2\right)\)

\(=\left(\frac{9}{25}-36\right):\left(\frac{19}{5}+0,2\right)\)

\(=\left(-\frac{891}{25}\right):4\)

\(=-\frac{891}{100}\)

b)\(\frac{5}{18}-1,456:\frac{7}{25}+4,5.\frac{4}{5}\)

\(=\frac{5}{18}-\frac{26}{5}+\frac{18}{5}\)

\(=-\frac{119}{90}\)

^...^  ^_^

\(-23-150+\left(-9\right)+1913\)

\(=1913-\left(23+150+9\right)\)

\(=1913-182\)

\(=1731\)

Lời giải:
a.

$-18: \frac{3}{5}=-18.\frac{5}{3}=-30$

b.

$\frac{3}{4}:(-9)=\frac{3}{4}.\frac{-1}{9}=\frac{-1}{12}$

c.

$\frac{13}{20}-\frac{6}{7}: \frac{10}{21}=\frac{13}{20}-\frac{6}{7}.\frac{21}{10}$

$=\frac{13}{20}-\frac{9}{5}=\frac{13}{20}-\frac{36}{20}=\frac{-23}{20}$

d.

$\frac{-21}{5}: (\frac{7}{3}.\frac{7}{5})=\frac{-21}{5}: \frac{49}{15}$

$=\frac{-21}{5}.\frac{15}{49}=\frac{-9}{7}$

e.

$(\frac{-2}{5}+\frac{1}{4}): (1-\frac{2}{5})$

$=\frac{-3}{20}: \frac{3}{5}=\frac{-1}{4}$