Câu 26:

\(A=\left(2\sqrt{7}-2\sqrt{3}-\sqrt{7}\right)\sqrt{7}+2\sqrt{21}\\ =\left(\sqrt{7}-2\sqrt{3}\right)\sqrt{7}+2\sqrt{21}=7-2\sqrt{21}+2\sqrt{21}=7\\ B=\sqrt{\dfrac{3}{75}}=\sqrt{\dfrac{1}{25}}=\dfrac{1}{5}\)

Câu 27:

\(a,\Leftrightarrow\sqrt{x}=4\Leftrightarrow x=16\\ b,\Leftrightarrow\sqrt{\left(x-2\right)^2}=3\Leftrightarrow\left|x-2\right|=3\\ \Leftrightarrow\left[{}\begin{matrix}x=3+2=5\\x=-3+2=-1\end{matrix}\right.\)

Câu 28:

\(a,\left\{{}\begin{matrix}x=\dfrac{6^2}{3}=12\\y=\sqrt{x\left(x+3\right)}=\sqrt{12\cdot15}=10\sqrt{3}\end{matrix}\right.\\ b,\left\{{}\begin{matrix}BC=\dfrac{AC}{\sin B}=\dfrac{5}{\sin50}\approx6,5\left(cm\right)\\AB=\sqrt{BC^2-AC^2}\approx4,2\left(cm\right)\end{matrix}\right.\)

Ex2 :

1. Phong said he wanted some coffee

2. Nam and Minh said they take a taxi to there

4. My mother asked me I was doing my homework.

5. I asked him what he was name

???

lx 

\(b\)

B nhé

Lời giải:

a.

$(-6)+|83|-(-75)+|-37|=-6+83+75+37=-6+195=195-6=189$

b.

$(-12)-(-26)-[(-9)-|21|)=-12+26-(-9-21)=-12+26+(9+21)$

$=-12+26+30=-12+56=56-12=44$

c.

$15-(-48)-15+(-17)-|-48|=15+48-15-17-48$

$=(15-15)+(48-48)-17=-17$

d.

$-24-(-33)+|24|-(-|78|)-|33|-78$

$=-24+33+24+78-33-78$

$=(-24+24)+(33-33)+(78-78)=0$

thanks bro

Đăng từng câu i pro:))

Dài quá

A
B
C
A
C
C
D
B
A
C

Very so ez

R 

Sáng nay là môn cuối ròi

'-'

rồi <3, nhẹ :)

Sắp rồi anh ạ

mai mik thi nhaaaaaa :3