a)
4x+x²-x²=4-4
4x=0
x=0
b)
\(x^2+24=x^2-12x+36\)
\(x^2-x^2+12x=36-24\)
12x=12
x=1

a)
\(x^2-6x+9-4=0\)
\(x^2-6x+5=0\)
\(x^2-x-5x+5=0\)
\(x\left(x-1\right)-5\left(x-1\right)=0\)
(x-5)(x-1)=0
x-5=0  hoặc  x-1=0
x=5     hoặc   x=1
b)
\(\left(x-5-x-3\right)\left(x-5+x+3\right)=0\)
\(-8.\left(2x-2\right)=0\)
\(-8.2\left(x-1\right)=0\)
x-1=0
x=1

20)
(2n+8)\(⋮\)(n+3)
2(n+4)\(⋮\)(n+3)
=>2\(⋮\)(n+3)
n+3\(\in\) Ư(2)={1;-1;2;-2}
n=-1;-2;-4;-5

bài 2
c)
\(\dfrac{x}{y}=\dfrac{5}{4}=>\dfrac{x}{5}=\dfrac{y}{4}=\dfrac{x+y}{5+4}=\dfrac{18}{9}=2\)
x=10
y=8
d)
\(\dfrac{x}{3}=\dfrac{y}{4}=>\dfrac{2x}{6}=\dfrac{5y}{20}=\dfrac{2x+5y}{6+20}=\dfrac{10}{26}=\dfrac{5}{13}\)
x=15/13
y=20/13

d

A=\(2^2-9^3+4^{-2}.16-2.5^2\)
\(=4-729+1-50=-774\)
B=\(\left(2^3.2\right).\dfrac{1}{2}+3^{-2}.3^2-7.1+5\)
\(B=2^4.\dfrac{1}{2}+1-7+5=8+1-7+5=7\)
 

2 người

1)
\(\left[\dfrac{\sqrt{x}\left(\sqrt{x}+1\right)}{x-1}+\dfrac{\sqrt{x}\left(\sqrt{x}-1\right)}{x-1}\right]:\dfrac{2\sqrt{3x}}{x-1}\)
\(=\left(\dfrac{x+\sqrt{x}+x-\sqrt{x}}{x-1}\right).\dfrac{x-1}{2\sqrt{3x}}\)
\(=\dfrac{2x}{x-1}.\dfrac{x-1}{2\sqrt{3x}}=\dfrac{\sqrt{x}}{\sqrt{3}}=\dfrac{\sqrt{3x}}{3}\)

tam giác ABC vuông tại A có
*AH²=BH.CH
25=x.x
x²=25
x=5
=> BC= 2x=2.5=10
*  AC.AB=AH.BC
   y.y=5.10
   y²=50
   y=5\(\sqrt{2}\)

\(=\dfrac{9}{49}.\dfrac{-343}{27}=-\dfrac{7}{3}\)