Hàm số nào sau đây đồng biến trên R?

A.  y = 3 tan x

B.  y = 2 x 4 + x 2

C.  y = x 3 - 3 x - 1

D.  y = x 3 + 2018

What did you do last weekend?

Tomorrow,I will study Unit3

We should'nt eat too much fast food

If the weather is fine,we will have a picnic next sunday

My hobby is carving eggshells and until I have carved nearly 100

Last Tuesday , he went home late because there are a traffic jame near his house

Going home from shool yesterday, I helped an old man to go across the street

Where did her uncle live five months ago?

We hate staying all day

Lan never eatsBanh tet.She will try some thí year

*ta có:

\(\dfrac{1+2y}{18}\)=\(\dfrac{1+4y}{24}\)

<=>(1+2y).24=18.(1+4y)

<=>24+48y =18+72y

<=>24-18 = 72y-48y

<=>6 = 24y

<=> y =\(\dfrac{1}{4}\)

* Thay y=\(\dfrac{1}{4}\)vào tỉ lệ thức\(\dfrac{1+4y}{24}\)=\(\dfrac{1+6y}{6x}\),ta có:

\(\dfrac{1+4^{\dfrac{1}{4}}}{18}\)\(\)=\(\dfrac{1+6\dfrac{1}{4}}{6x}\)

<=>\(\dfrac{1+1}{24}\)=\(\dfrac{1+\dfrac{3}{2}}{6x}\)

<=>\(\dfrac{1}{12}\)=\(\dfrac{\dfrac{5}{2}}{6x}\)

<=>\(\dfrac{1}{12}\)=\(\dfrac{5}{12x}\)

<=>12.5=12x

<=>x=5

Vậy x=5;y=\(\dfrac{1}{4}\)

<=>-7-x+12=-13+7

<=>-7-x+12=-6

<=>-7-x =-18

<=> x =11

Vậy x=11

<=>2+x-13=-2

<=>2+x=11

<=>x=9

Vậy x=9