B

câu 1/ 5x(\(4x^2\)-2x+1) - 2x(\(10x^2\)-5x-2)

= 5x.\(4x^2\)-5x.2x+ 5x.1 - ( 2x.\(10x^2\)-2x.5x-2x.2)

= 9\(x^3\)-10\(x^2\)+5x - 20\(x^3\)+10\(x^2\)+4x

= (9\(x^3\)-\(20x^3\)) + (-10\(x^2\)+10\(x^2\)) + (5x+4x)

= \(-11x^3\) + 9x

à cj ơi, e 2k6, đọc phần lí thuyết r lm, nên có lỗi sai j mong cj thông cảm

5x.( 4x²-2x+1)- 2x( 10x²-5x-2)

= 20x³- 10x²+5x - 20x³+ 10x²+ 4xx

= (5x+4x)= 9x

Thay x=3 vào 9x, ta có:

9×3=27

Vậy biểu thức trên bằng 27

a: 2x^2y-50xy=2xy(x-25)

b: 5x^2-10x=5x(x-2)

c: 5x^3-5x=5x(x^2-1)=5x(x-1)(x+1)

d: \(x^2-xy+x=x\left(x-y+1\right)\)

e: x(x-y)-2(y-x)

=x(x-y)+2(x-y)

=(x-y)(x+2)

f: 4x^2-4xy-8y^2

=4(x^2-xy-2y^2)

=4(x^2-2xy+xy-2y^2)

=4[x(x-2y)+y(x-2y)]

=4(x-2y)(x+y)

f1: x^2ỹ-y^2+y

=(x-y)(x+y)+(x+y)

=(x+y)(x-y+1)

1. a) \(( 5x-1)^2 - (5x-4) ( 5x+4) = 7\)

\(\Leftrightarrow\)\(25x^2-10x+1-(25x^2-16)=7\)

\(\Leftrightarrow\)\(25x^2-10x+1-25x^2+16-7=0\)

\(\Leftrightarrow\)\(10x=10\)

\(\Rightarrow x=1\)

b) \(( 4x-1)^2 - (2x+3)^2 + 5(x+2)^2 + 3(x-2) ( x+2) = 500\)

\(\Leftrightarrow\)\(16x^2-8x+1-4x^2-12x-9+5x+10+3x^2-12=500\)

\(\Leftrightarrow\)\(15x^2-15x=510\)

\(\Leftrightarrow\)\(15(x^2-x)=510\)

\(\Leftrightarrow\)\(x^2-x=34\)

\(\Rightarrow x=-5,352349955\)

c) \((x-2)^3 - (x-2) ( x^2+2x+4 ) + 6(x-2)(x+2) = 60\)

\(\Leftrightarrow x^3-6x^2+12x-8-\left(x^3-2^3\right)+6\left(x^2-4\right)=60\)

\(\Leftrightarrow x^3-6x^2+12x-8-x^3+8+6x^2-24=60\)

\(\Leftrightarrow12x-24=60\)

\(\Leftrightarrow12x=84\)

\(\Rightarrow x=7\)

Lời giải:
a.

$A=20x^3-10x^2+5x-(20x^3-10x^2-4x)$

$=9x=9.15=135$

b.

$B=(5x^2-20xy)-(4y^2-20xy)=5x^2-4y^2$

$=5(\frac{-1}{5})^2-4(\frac{-1}{2})^2=\frac{-4}{5}$

c.

$C=(6x^2y^2-6xy^3)-(8x^3-8x^2y^2)-(5x^2y^2-5xy^3)$

$=-8x^3+9x^2y^2-xy^3$

$=(-2x)^3+(3xy)^2-xy^3$

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

\(5x^4y+10x^3y+10x^2y^3+5xy^4\)

\(=5xy.x^3+5xy.2x^3+5xy.2xy^3+5xy.y^3\)

\(=5xy\left(x^3+2x^3+2xy^3+y^3\right)\)

Ht pt