Chọn C

Bài 1: 

a) \(-5\left(x^2-3x+1\right)+x\left(1+5x\right)=x-2\)

\(\Rightarrow-5x^2+15x-5+x+5x^2=x-2\)

\(\Rightarrow16x-5=x-2\)

\(\Rightarrow16x-x=5-2\)

\(\Rightarrow15x=3\)

\(\Rightarrow x=\dfrac{15}{3}=5\)

b) \(12x^2-4x\left(3x+5\right)=10x-17\)

\(\Rightarrow12x^2-12x^2-20x=10x-17\)

\(\Rightarrow-20x=10x-17\)

\(\Rightarrow-20x-10x=-17\)

\(\Rightarrow-30x=-17\)

\(\Rightarrow x=\dfrac{-30}{-17}=\dfrac{30}{17}\)

c) \(-4x\left(x-5\right)+7x\left(x-4\right)-3x^2=12\)

\(\Rightarrow-4x^2+20x+7x^2-28x-3x^2=12\)

\(\Rightarrow-8x=12\)

\(\Rightarrow x=\dfrac{12}{-8}=-\dfrac{4}{3}\)

Bài 2: 

a) \(\left(x+5\right)\left(x-7\right)-7x\left(x-3\right)\)

\(=x^2-7x+5x-35-7x^2+21x\)

\(=-6x^2+19x-35\)

b) \(x\left(x^2-x-2\right)-\left(x-5\right)\left(x+1\right)\)

\(=x^3-x^2-2x-x^2+x-5x-5\)

\(=x^3-2x^2-6x-5\)

c) \(\left(x-5\right)\left(x-7\right)-\left(x+4\right)\left(x-3\right)\)

\(=x^2-7x-5x+35-x^2-3x+4x-12\)

\(=11x+23\)

d) \(\left(x-1\right)\left(x-2\right)-\left(x+5\right)\left(x+2\right)\)

\(=x^2-2x-x+2-x^2+2x+5x+10\)

\(=4x+12\)

b: \(\Leftrightarrow\dfrac{x-2}{A}=\dfrac{\left(5x-1\right)\left(x-2\right)}{x^2\left(5x-1\right)+3\left(5x-1\right)}=\dfrac{x-2}{x^2+3}\)

hay \(A=x^2+3\)

a) \(2+2+2+2+2=2\times5=10\)

\(2\times5=10\)

\(5+5=2\times5=10\)

\(5\times2=10\)

b) \(3\times5=3+3+3+3+3=15\)

\(5\times3=5+5+5=15\)

\(3\times5=5+5+5=15\)

\(5\times3=3+3+3+3+3=15\)

a) 2 + 2 + 2 + 2 + 2 = 10
    2 x 5 = 10
    5 + 5 = 10
    5 x 2 = 10
b) 3 x 5 = 3 + 3 + 3 + 3 + 3 = 15
    5 x 3 = 5 + 5 + 5 = 15
    3 x 5 = 15
    5 x 3 = 15

\(a,=5x-10+2x+6=7x-4\\ b,=x^2+2x+1-x^2+3x+10=5x+11\\ c,=x^2-49-x^2+1=-48\\ d,\text{Đề có sai ko vậy?}\)

a, \(\left(x+2\right)^2-\left(x+3\right)\left(x-3\right)+10=x^2+4x+4-x^2+9+10=4x+23\)

b, \(\left(5-x\right)^2+\left(x+5\right)^2-\left(2x+10\right)\left(x-5\right)=25-10x+x^2+x^2+10x+25-2x^2+50=100\)

a) ( x + 2 )² - ( x + 3 )( x - 3 ) + 10 

= x² + 4x + 4 - ( x² - 9 ) + 10

= x² + 4x + 4 - x² + 9 + 10

= 4x + 23

b) ( x + 1 )² + ( x - 2 )( x + 3 ) - 4x

= x² + 2x + 1 + x² + x - 6 - 4x

= 2x² - 2x - 5

c) ( x - 2 )( x + 2 ) - ( x - 3 )( x + 1 )

= x² - 4 - ( x² - 2x - 3 )

= x² - 4 - x² + 2x + 3

= 2x - 1 

d) ( x + 4 )² + ( x + 5 )( x - 5 ) - 2x( x + 1 )

= x² + 8x + 16 + x² - 25 - 2x² - 2x

= 6x - 9

e) ( 5 - x )² + ( x + 5 )² - ( 2x + 10 )( x - 5 )

= 25 - 10x + x² + x² + 10x + 25 - ( 2x² - 50 ) 

= 2x² + 50 - 2x² + 50

= 100

f) ( x - 2 )² + ( x + 1 )² + 2( x - 2 )( -1 - x )

= x² - 4x + 4 + x² + 2x + 1 + 2( -x² + x + 2 )

= 2x² - 2x + 5 - 2x² + 2x + 4

= 9

g) ( 3x - 5 )² - 2( 3x - 5 )( 3x + 5 ) + ( 3x + 5 )²

= [ ( 3x - 5 ) - ( 3x + 5 ) ]²

= ( 3x - 5 - 3x - 5 )²

= ( -10 )² = 100

h) (  y - 3 )( y + 3 )( y² + 9 ) - ( y² + 2 )( y² - 2 )

= ( y² - 9 )( y² + 9 ) - [ ( y² )² - 4 ]

= [ ( y² )² - 81 ] - y⁴ + 4

= y⁴ - 81 - y⁴ + 4

= -77

Tks bạn ✿Trần Nhật Quỳnh²⁰⁰⁷✿

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