i)  ta có tỉ lệ thức : 14/10=21/15

10/14=15/21

10/15=14/21

14/10=21/15 

i ) 14/10 = 21/15 ; 10/14 = 15/21 ; 15/10 = 21/14 ; 10/15 = 14/21

ii ) AB/2 = 3/CD ; 2/AB = CD/3 ; CD/2 = 3/AB ; 2/CD = AB/3 

iii ) AB/EF = GH/CD ; EF/AB = CD/GH ; CD/EF = GH/AB ; EF/CD = AB/GH

iv ) 4/5 = MN/AB ; 5/4 = AB/MN ; AB/5 = MN/4  ; 5/AB = 4/MN 

a, 2(x + 1) + 3(x - 4 ) = 0

=> 2x + 2 + 3x - 12 = 0

=> 5x - 10 = 0

=> x = 2

b, 9x^2 - 16 = 0

=> 9x^2 = 16

=> x^2 = 16/9

=> x = +- 4/3

c, 2x^2 + 7x - 9 = 0

=> 2x^2 - 2x + 9x - 9 = 0

=> 2x(x - 1) + 9(x - 1) = 0

=> (2x + 9)(x - 1) = 0

=> x = -9/2 hoac x = 1

bài 1

ta có : \(\left(x+\frac{1}{2}\right)^2\ge0\Rightarrow\left(x+\frac{1}{2}\right)^2+\frac{5}{4}\ge\frac{5}{4}\)

bài 2 . ta có :

\(M=x^2\left(x+y-3\right)-y\left(x+y-3\right)+x+y+2019=0-0+3+2019=2022\)

\(\left(20^{2016}+11^{2016}\right)^{2017}>\left(20^{2016}+11^{2016}\right)^{2016}.20^{2016}\)

\(=\left(20.20^{2016}+20.11^{2016}\right)^{2016}>\left(20^{2017}+11^{2017}\right)^{2016}\)

Ta có: 9⁹⁹ = 9^{11 . 9} = (9¹¹)⁹

Do 9¹¹ > 99 <=> (9¹¹)⁹ > 99⁹

<=> 9⁹⁹ > 99⁹.

Vậy 9⁹⁹ > 99⁹.

ta có :

\(\hept{\begin{cases}9^{99}=\left(9^{11}\right)^9\\99^9< \left(9^3\right)^3\end{cases}}\) vì vậy \(99^9< 9^{99}\)

Mn ơi giúp mik vs

1.8 trieu dong  

2. 6 trieu dong

3.5 trieu dong

\(125x^3-\frac{1}{27}y^3=\left(5x-\frac{1}{3}y\right)=\left(25x^2+\frac{5}{3}xy+\frac{1}{9}y^2\right)\)

\(\left(x+\frac{1}{2}\right)\left(x^2-\frac{x}{2}+\frac{1}{4}\right)=x^3+\frac{1}{8}\)

tỉ số x/y=2/7

nhân chéo 2 vế -> pt <-> (x-2)(y+7)=(y-7)(x+2)

                                  <-> xy+7x-2y-14=xy+2y-7x-14

                                   <-> 14x=4y

                                    <-> x/y = 2/7