a)
\(=\left(x+2y\right)\left(x^2-xy+y^2\right)-3xy\left(x+2y\right)\)
\(=\left(x+2y\right)\left(x^2-xy+y^2-3xy\right)\)
\(=\left(x+2y\right)\left(x^2-2xy+y^2\right)\)
\(=\left(x+2\right)\left(x-2\right)^2\)
b)
\(3x\left(2x-1\right)\left(2x+1\right)=0\)
3x=0 =>x=0
hoặc 2x-1=0 => 2x=1=>x=1/2
hoặc 2x+1=0=>2x=-1=>x=-1/2

1

a)
\(x\left(x-1\right)+2\left(x-1\right)=0\)
(x+2)(x-1)=0
x+2=0 hoặc x-1=0
x=-2 hoặc x=1
b)
\(5x\left(x-2021\right)-x+2021+1-1=0\)
5x(x-2021)-(x-2021)=0
(5x-1)(x-2021)=0
5x-1=0 hoặc x-2021=0
x=1/5  hoặc x=2021
 

=>\(\dfrac{2x}{16}=\dfrac{y}{5}=\dfrac{z}{6}=\dfrac{2x+y-z}{15}=\dfrac{-30}{15}=-2\)
x=-16
y=-10
z=-12

c
a
a
b
a

1

bài 1
\(\left(-\dfrac{1}{3}\right)^3=\dfrac{-1}{27}\)
\(\left(-0,3\right)^2=0,09\)
\(\left(-5\dfrac{1}{2}\right)^0=\left(\dfrac{-11}{2}\right)^0=1\)
\(\left(\dfrac{-1}{2}\right)^4=\dfrac{1}{16}\)
bài 2
\(2=2^1\)
\(8^2=\left(2^3\right)^2=2^6\)
\(\left(4.2^5\right):16=\left(2^2.2^5\right):2^4=2^7:2^4=2^3\)

tam giác ABC vuông tại A đường cao AH có
* AC²=BC²-AB²
  AC² = 100-36=64
  AC=8cm
* AC²=HC.BC
  64=HC.10
  HC=6,4cm

\(A=x^3+2x^2+4x-2x^2-4x-8-128-x^3\)
\(A=-136\)
\(B=\left(2x+3y\right)\left(2x-3y\right)^2-\left(3x-2y\right)\left(3x+2y\right)^2\)
\(B=\left(2x+3y\right)\left(2x-3y\right)\left(2x-3y\right)-\left(3x-2y\right)\left(3x+2y\right)\left(3x+2y\right)\)
\(B=\left(4x^2-9y^2\right)\left(2x-3y\right)-\left(9x^2-4y^2\right)\left(3x+2y\right)\)
\(B=8x^3-12x^2y-18xy^2-27y^3-27x^3-18x^2y+12xy^2+8y^3\)
\(B=-19x^3-30x^2y-6xy^2-19y^3\)
\(B=-19\left(x^3-y^3\right)-6xy\left(5x+y\right)\)

bài 5
đoàn xe trở số tấn gạo là
20,25x18=364,5 tấn
bài 6
chu vi HCN là
(16,2+9,3)x2=51 cm²
bài 8 
chu vi tam giác là
6,5x4=26 m²