TA có: \(y=-x^4+4x^2-3\)

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

               \(=-\left(x^2-1\right)^2+1\le1\)

Vì \(y\in\left[-2;3\right]\) 

=>..........................

Đến đây dễ rồi bạn tự làm nốt nhé

Ta có : 0,9999... = 3 . 0,33333....  

                           = \(\frac{1}{3}.3\)

                           = 1 

Vậy 0,9999... = 1 (đpcm)

Đặt x = 0,(9).
Ta có 10x = 9,(9).
Lấy 10x – x thì 10x – x = 9,(9) – 0,(9).
Điều này có nghĩa là 9x = 9 hay x = 1.
Vậy 0,(9) = 1.

1) Tom thinks making models is interesting

2) My father thinks carving eggshells is unusual

3) .... making pottery boring

4) tương tự..............

1)  Tom finds making models interesting.

--> Tom thinks....making models is interesting....................................................

2)  My father finds carving eggshells unusual.

--> My father thinks...carving eggshells is unusual...................................................

3)  Peter thinks making pottery is boring.

--> Peter finds......making pottery boring................................................

4)  Hang thinks reading books is useful.

--> Hang finds......reading books  useful.......................................................

5)  Hoang s ice-skating best

--> Ice-skating is.....Hoang 's favourite sport...............................................

6) Mary started her hobby five years ago.

--> Mary began.....her hobby ...five years ago.....................................................

7)  Hong began collecting stamps when she was 5.

--> Hong started.......collecting stamps when she was 5.............................................

8)  Binh intends to travel around the world.

--> Binh plans.. travelling around the world.............................................

9)  We intend to clean the pond in the school yard.

--> We plant......cleaning the pond in the school yard.....................................................

\(Q=\frac{a^4}{ab+ca}+\frac{b^4}{ab+bc}+\frac{c^4}{bc+ca}\ge\frac{\left(a^2+b^2+c^2\right)^2}{2\left(ab+bc+ca\right)}\)

\(\ge\frac{\left(a^2+b^2+c^2\right)\left(ab+bc+ca\right)}{2\left(ab+bc+ca\right)}\ge\frac{\frac{\left(a+b+c\right)^2}{3}}{2}\ge\frac{1}{6}\)

Dấu "=" xảy ra khi \(a=b=c=\frac{1}{3}\)