chỉ với

\(-\dfrac{3}{7}.\dfrac{5}{7}+\left(-\dfrac{5}{7}\right).\dfrac{8}{11}+\dfrac{19}{7}\\ =\dfrac{5}{7}.\left(-\dfrac{3}{7}-\dfrac{8}{11}\right)+\dfrac{19}{7}\\ =\dfrac{5}{7}.-\dfrac{89}{77}+\dfrac{19}{7}\\ =\dfrac{445}{539}+\dfrac{19}{7}\\ =\dfrac{1908}{539}\)

`#3107.101107`

`x^2 - 0,04 = 0`

`\Rightarrow x^2 = 0,04`

`\Rightarrow x^2 = (+-0,2)^2`

`\Rightarrow x = +- 0,2`

Vậy, `x \in {-0,2; 0,2}.`

`#3107.101107`

c)

$-x + \dfrac{3}2 = x + \dfrac{3}5$

$\Rightarrow -x - x = \dfrac{3}5 - \dfrac{3}2$

$\Rightarrow -2x = -\dfrac{9}{10}$

$\Rightarrow 2x = \dfrac{9}{10}$

$\Rightarrow x = \dfrac{9}{10} \div 2$

$\Rightarrow x = \dfrac{9}{20}$

Vậy, $x = \dfrac{9}{20}.$

Ta có:

∠COD + ∠COB + ∠BOA = 180⁰

⇒ ∠COB = 180⁰ - (∠COD + ∠BOA)

= 180⁰ - (30⁰ + 20⁰)

= 180⁰ - 50⁰

= 130⁰

Bài 1:

Dường chéo của tv là:48.2,54=121,92(cm)xấp xỉ 121,9 cm

Bài 2:

a  3x+1/4=5/4

    3x     =5/4-1/4

     3x=  1

     x=1:3

    x=1/3

b   (x-3)^2=36

    (x-3)^2=6^2

    x-3 = 6

   x  =6+3

   x=9

\(3^x=9^3.27^5=\left(3^2\right)^3.\left(3^3\right)^5\\ =>3^x=3^{2.3}.3^{3.5}\\ =>3^x=3^6.3^{15}=3^{6+15}=3^{21}\\ =>x=21\)

3^x=9³x27⁵

3^x=(3²)³x(3³)⁵

3^x=3²¹

vậy x=3²¹

\(\sqrt{x^2}=9\\ \Rightarrow x=9.\)

x=9 hoặc -9 nha