Lời giải:

$=15.7-34(-7)-(-7).48$

$=15.7+34.7+48.7$

$=7(15+34+48)=7.97=679$

a) \(\dfrac{1}{3}+\dfrac{3}{5}+\dfrac{1}{15}-\dfrac{3}{4}-\dfrac{2}{9}-\dfrac{1}{36}+\dfrac{1}{72}\)

\(=\dfrac{5+9+1}{15}-\dfrac{27+8+1}{36}+\dfrac{1}{72}=1-1+\dfrac{1}{72}=\dfrac{1}{72}\)

b) \(=\dfrac{1}{5}-\dfrac{1}{5}-\dfrac{3}{7}+\dfrac{3}{7}+\dfrac{5}{9}-\dfrac{5}{9}-\dfrac{1}{11}+\dfrac{1}{11}+\dfrac{7}{13}-\dfrac{7}{13}-\dfrac{9}{16}\)

\(=\dfrac{9}{16}\)

\(\dfrac{5}{9}-\dfrac{1}{4}=\dfrac{20}{36}-\dfrac{9}{36}=\dfrac{11}{36}\)

\(\dfrac{49}{50}-\dfrac{4}{25}=\dfrac{49}{50}-\dfrac{8}{50}=\dfrac{41}{50}\)

help help !!

11/36

41/50

Bài 2:

a) 11. x = -55

x = -55 : 11

x = -5

Vậy x = -5

b) -3 . x = -12

x = -12 : (-3)

x = 4

Vậy x = 4

c) 3x - 12 = -48

3x = -48 + 12

3x = -36

x = -36 : 3

x = -12

Vậy x = -12

d) 10 + 23 . (2x - 10) = -36

23 . (2x - 10) = -36 - 10

23 . (2x - 10) = -46

2x - 10 = -46 : 23

2x - 10 = -2

2x = -2 + 10

2x = 8

x = 8: 2

x = 4

Vậy x = 4

f) | 2x - 1| + 3 = 8

|2x - 1| = 8 - 3

|2x - 1| = 5

\(\Rightarrow\left[\begin{matrix}2x-1=5\\2x-1=-5\end{matrix}\right.\Rightarrow\left[\begin{matrix}2x=6\\2x=-4\end{matrix}\right.\Rightarrow\left[\begin{matrix}x=3\\x=-2\end{matrix}\right.\)

Vậy x = 3 hoặc x = -2

g) |2x² - 3| - 4 = 11

|2x²- 3| = 11 + 4

|2x² - 3| = 15

\(\Rightarrow\left[\begin{matrix}2x^2-3=15\\2x^2-3=-15\end{matrix}\right.\Rightarrow\left[\begin{matrix}2x^2=18\\2x^2=-12\end{matrix}\right.\Rightarrow\left[\begin{matrix}x^2=9\\x^2=-6\end{matrix}\right.\Rightarrow\left[\begin{matrix}x^2=3^2\\\left(loại\right)\end{matrix}\right.\Rightarrow\left[\begin{matrix}x=3\\\end{matrix}\right.\)

Vậy x = 3.

Bài 1:

\((-48) . 72 +36 . (-304) \)

\(=\left[\left(-48\right).\left(36.2\right)\right]+36.\left(-340\right)\)

\(=\left[\left(-48\right).2\right].36+36.\left(-340\right)\)

\(=\left(-96\right).36+36.\left(-304\right)\)

\(=36.\left[\left(-96\right)+\left(-304\right)\right]\)

\(=36.\left(-400\right)\)

\(=-14400\)

a,2 giờ 40 phút +25 phút nhân 3

b, 5 giờ 12 phút nhân 2 - 4 giờ

c,[ 2 giờ 45 phút +49 phút ] nhân 4

d,[ 8 giờ 15 phút ] :5 + 1 giờ 24 phút

7^2 . 7^x = 7^4

7^x = 7^2

=> x= 2

49 . 7^X = 2401

<=> 7² . 7^X  = 7⁴

=> 7^X = 7⁴ : 7²

<=> 7^X = 7² => X= 2

\(7^x=\frac{2401}{49}\)

\(7^x=49\)

\(7^x=7^2\)

x = 2

Giải:

a) Ta có:

\(7^6+7^5-7^4\)

\(=7^4\left(7^2+7-1\right)\)

\(=7^4.55⋮55\)

Vậy ...

b) Ta có:

\(16^5+2^{15}\)

\(=\left(2^4\right)^5+2^{15}\)

\(=2^{20}+2^{15}\)

\(=2^{15}\left(2^5+1\right)\)

\(=2^{15}.33⋮33\)

Vậy ...

c) \(81^7-27^9-9^{13}\)

\(=\left(3^4\right)^7-\left(3^3\right)^9-\left(3^2\right)^{13}\)

\(=3^{28}-3^{27}-3^{26}\)

\(=3^{26}\left(3^2-3-1\right)\)

\(=3^{26}.5⋮5⋮405\)

Vậy ...

Chúc bạn học tốt!

a) 7⁶ +7⁵ -7⁴

=7⁴.7² +7⁴.7-7⁴

=7⁴.(7²+7-1)

=7⁴.55⋮55

b) 16⁵+2¹⁵

=(2⁴)⁵ +2¹⁵

=2²⁰+2¹⁵

=2¹⁵.2⁵+2¹⁵

=2¹⁵.(2⁵+1)

=2¹⁵.33⋮33

c)81⁷-27⁹-9¹³

=(3⁴)⁷-(3³)⁹......(làm tương tự)

Cảm ơn các bạn nhiều, chúng mình làm bạn nha?

\(\Leftrightarrow\left(\dfrac{13}{4}-x\right)\cdot\dfrac{101}{25}-\dfrac{1213}{100}=2\cdot\left[\left(x-\dfrac{10}{7}\right)\cdot\dfrac{49}{50}+\dfrac{2}{5}\right]\)

\(\Leftrightarrow\left(\dfrac{13}{4}-x\right)\cdot\dfrac{101}{25}=\dfrac{49}{25}\left(x-\dfrac{10}{7}\right)+\dfrac{4}{5}+\dfrac{1213}{100}\)

\(\Leftrightarrow\dfrac{1313}{100}-\dfrac{101}{25}x=\dfrac{49}{25}x-\dfrac{490}{175}+\dfrac{1293}{100}\)

=>-6x=13/5

hay x=-13/30