\(\begin{array}{*{20}{c}}{a)\,\,}\\{}\\{}\end{array}\begin{array}{*{20}{c}}{ + \begin{array}{*{20}{c}}{28}\\{35}\end{array}}\\\hline{\,\,\,\,63}\end{array}\)                      \(\begin{array}{*{20}{c}}{ - \begin{array}{*{20}{c}}{63}\\{28}\end{array}}\\\hline{\,\,\,\,35}\end{array}\)                     \(\begin{array}{*{20}{c}}{ - \begin{array}{*{20}{c}}{63}\\{35}\end{array}}\\\hline{\,\,\,28}\end{array}\)

\(\begin{array}{*{20}{c}}{b)\,\,}\\{}\\{}\end{array}\begin{array}{*{20}{c}}{ + \begin{array}{*{20}{c}}{42}\\{49}\end{array}}\\\hline{\,\,\,\,91}\end{array}\)                     \(\begin{array}{*{20}{c}}{ - \begin{array}{*{20}{c}}{91}\\{42}\end{array}}\\\hline{\,\,\,49}\end{array}\)                       \(\begin{array}{*{20}{c}}{ - \begin{array}{*{20}{c}}{91}\\{49}\end{array}}\\\hline{\,\,\,\,42}\end{array}\)

91 x 157 -  29 x 91 - 91 x 28

=9100

127 x 63 + 19 x 127 - 82 x 26

=8282

2 x 9 x 41 + 36 + 3 x 57 x 6

=1800

29 x 17 + 31 x 29 + 48 x 93 - 48 x 22

=4800

1125 - 25 x 30 + 0,06 : 0,2

=375.3

Bn k cho mk nha!

91 x 157 -  29 x 91 - 91 x 28

= 19 (157 - 29 - 28)

=19 * 100

=1900

127 x 63 + 19 x 127 - 82 x 26

= 127 (63 + 19) - 82 * 26

= 127 * 82 - 82 * 26

= 82 (127 - 26)

= 82 * 101

= 8282

2 x 9 x 41 + 36 + 3 x 57 x 6

= 738 + 36 + 1026

= 1800 

29 x 17 + 31 x 29 + 48 x 93 - 48 x 22

= 29 (17 + 31) + 48 (93 - 22)

= 29 * 48 + 48 * 71 

= 48 (29 + 71) 

= 48 * 100

= 4800

1125 - 25 x 30 + 0,06 : 0,2

= 1125 - 750 + 0,3

= 375 + 0,3

= 375,3

GIẢI

  91 x 157 - 29 x 91 - 91 x 28

=91 x (157 + 29 + 91)

=91 x 277

=25207

  127 x 63 + 19 x 127 - 82 x 26

= 127 x (63 +19) - 2132

= 127 x   92        - 2132

= 11684              - 2132

=  9552

  29 x 17 + 31 x 29 + 48 x 93 - 48 x 22

=29 x(17 +31)        + 48 x(93 - 22)

=29 x 48                + 48 x71

=48 x (29 + 71)

=48 x 100

=4800

  1125 - 25 x 30 + 0,06 : 0,2

= 1100       x 30 + 0,3

= 33000             +0,3

= 33000,3

 K HỘ MIK NGHEN

Ta có : 78/91 : 63/79 = 158/147 . Vì 158/147 > 1 => 78/91 > 63/79

Bỏ dấu ngoặc rồi tính:

a)(2015-79+19)-(-79+19)

b)-(515-80+91)-(2020+80-91)

Giải:

a,Ta có:(2015-79+19)-(-79+19)=2015-79+19+79-19

=2015-79+79+19-19

=2015+0+0=2015

b,-(515-80+91)-(2020+80-91)=-515+80-91-2020-80+91

=-515-2020+80-80-91+91

=-2535+0+0=-2535

a) (2015-79+19)-(-79+19)

= 2015 - 79 +19 + 79 -19

= 2015 + (79- 79) + (19 -19)

= 2015

b) - (515 - 80 +91) -(2020 +80-91)

= -515 + 80 - 91 - 2020 -80 +91

= -515 -2020 +( 80 -80) + (91 -91)

= -2535

Lời giải chi tiết:

84=80+4                    42=40+2                      55=50+5

77=70+7                    91=90+1                      39=30+9

28=20+8                    63=60+3                      99=90+9

\(\dfrac{9}{\sqrt{x-19}}+\dfrac{16}{\sqrt{y-5}}+\dfrac{25}{\sqrt{z-91}}=24-\sqrt{x-19}-\sqrt{y-5}-\sqrt{z-91}\\ \Leftrightarrow\left(\dfrac{9}{\sqrt{x-19}}+\sqrt{x-19}\right)+\left(\dfrac{16}{\sqrt{y-5}}+\sqrt{y-5}\right)+\left(\dfrac{25}{\sqrt{z-91}}+\sqrt{z-91}\right)=24\)

Áp dụng BDT: Cô-si:

\(\Rightarrow\left(\dfrac{9}{\sqrt{x-19}}+\sqrt{x-19}\right)+\left(\dfrac{16}{\sqrt{y-5}}+\sqrt{y-5}\right)+\left(\dfrac{25}{\sqrt{z-91}}+\sqrt{z-91}\right)\ge2\sqrt{\dfrac{9}{\sqrt{x-19}}\cdot\sqrt{x-19}}+2\sqrt{\dfrac{16}{\sqrt{y-5}}\cdot\sqrt{y-5}}+2\sqrt{\dfrac{25}{\sqrt{z-91}}\cdot\sqrt{z-91}}\\ =2\cdot3+2\cdot4+2\cdot5=24\)Dấu "=" xảy ra khi:\(\left\{{}\begin{matrix}\dfrac{9}{\sqrt{x-19}}=\sqrt{x-19}\\\dfrac{16}{\sqrt{y-5}}=\sqrt{y-5}\\\dfrac{25}{\sqrt{z-91}}=\sqrt{z-91}\end{matrix}\right.\Leftrightarrow\left\{{}\begin{matrix}x-19=9\\y-5=16\\z-91=25\end{matrix}\right.\Leftrightarrow\left\{{}\begin{matrix}x=28\\y=21\\z=116\end{matrix}\right.\)

Vậy các số \(\left\{x;y;z\right\}=\left\{28;21;116\right\}\)

9: \(=\dfrac{47}{51}\cdot\dfrac{17}{94}-\dfrac{47}{51}\cdot\dfrac{53}{91}-\dfrac{53}{91}\cdot\dfrac{91}{53}+\dfrac{53}{91}\cdot\dfrac{47}{51}\)

\(=\dfrac{1}{6}-1=-\dfrac{5}{6}\)

10: \(=\dfrac{13}{19}\cdot\dfrac{19}{26}-\dfrac{13}{19}\cdot\dfrac{71}{43}+\dfrac{71}{43}\cdot\dfrac{13}{19}-\dfrac{71}{43}\cdot\dfrac{86}{71}\)

\(=\dfrac{1}{2}-2=-\dfrac{3}{2}\)