812+36=812+612=1812=32

\(\dfrac{8}{12}+\dfrac{3}{6}=\dfrac{8}{12}+\dfrac{6}{12}=\dfrac{14}{12}=\dfrac{7}{6}\)

8/12 + 3/6 = 16/24 + 12/24 = 28/24 = 7/6

Ta có : 

\(\frac{8}{21}=\frac{2}{3}.\frac{4}{7}=\frac{-8}{7}.\frac{1}{-3}=\frac{2^2}{-7}.\frac{-2}{3}=...\)

Chúc bạn học tốt ~

\(b,N=\left(2x-1\right)^2-4\ge-4\\ N_{min}=-4\Leftrightarrow x=\dfrac{1}{2}\\ c,P=\left(2x-5\right)^2+6\left(2x-5\right)+9-4\\ P=\left(2x-5+3\right)^2-4=\left(2x-2\right)^2-4\ge-4\\ P_{min}=-4\Leftrightarrow x=1\\ d,Q=\left(x^2-2x+1\right)+\left(y^2+4y+4\right)+1\\ Q=\left(x-1\right)^2+\left(y+2\right)^2+1\ge1\\ Q_{min}=1\Leftrightarrow\left\{{}\begin{matrix}x=1\\y=-2\end{matrix}\right.\)

6a.

$M=x^2-x+1=(x^2-x+\frac{1}{4})+\frac{3}{4}$

$=(x-\frac{1}{2})^2+\frac{3}{4}\geq \frac{3}{4}$

Vậy $M_{\min}=\frac{3}{4}$ khi $x-\frac{1}{2}=0\Leftrightarrow x=\frac{1}{2}$

bài đây ạ  

3d:

20<x<45

x chia 4 dư 1 nên x-1 thuộc B(4)

=>\(x-1\in\left\{0;4;...;44;48\right\}\)

=>\(x\in\left\{1;5;...;45;49\right\}\)

mà 20<x<45

nên x thuộc {21;26;31;35;41}

4:

a: A={x∈N|51<=x<=127}

b: B={x∈N|100<=x<=999}

c: C={x∈N|x=7k+5; 0<=k<=8}

is your pen blue or green

is your computer grey or black

i love football because it's interesting

i love guitar because very easy

you so funny

you so interesting

Or: Do you like to eat pizza or hamburgers?

Do you like red or yellow?

Because: I like elephants because they are friendly.

I don't go to school today because I'm sick.

So: I like to eat apples so much.

Thank you so much!