`a)100x^2-20x+1`

`=(10x-1)^2`

Thay `x=1/10`

`=>100x^2-20x+1=(1-1)^2=0`

`b)49x^2-42x+10`

`=49*4/49-42*2/7+10`

`=4-12+10=2`

`c)25x^2+40x+16y^2`

`=(5x+4y)^2=(2+3)^2=25`

P=x3+y3+2xy=(x+y)3−3xy(x+y)+2xy=2013−601xy" role="presentation" style="border:0px; direction:ltr; display:inline-block; float:none; font-size:16.38px; line-height:0; margin:0px; max-height:none; max-width:none; min-height:0px; min-width:0px; padding:1px 0px; position:relative; white-space:nowrap; word-spacing:normal; word-wrap:normal" class="MathJax_CHTML mjx-chtml">P=x3+y3+2xy=(x+y)3−3xy(x+y)+2xy=2013−601xy

S=xy=x(201−x)" role="presentation" style="border:0px; direction:ltr; display:inline-table; float:none; font-size:16.38px; line-height:0; margin:0px; max-height:none; max-width:none; min-height:0px; min-width:0px; padding:1px 0px; position:relative; white-space:nowrap; word-spacing:normal; word-wrap:normal" class="MathJax_CHTML mjx-chtml">S=xy=x(201−x)

1≤x≤200" role="presentation" style="border:0px; direction:ltr; display:inline-block; float:none; font-size:16.38px; line-height:0; margin:0px; max-height:none; max-width:none; min-height:0px; min-width:0px; padding:1px 0px; position:relative; white-space:nowrap; word-spacing:normal; word-wrap:normal" class="MathJax_CHTML mjx-chtml">1≤x≤200

S=200−(x−1)(x−200)≥0⇒Smin=200" role="presentation" style="border:0px; direction:ltr; display:inline-block; float:none; font-size:16.38px; line-height:0; margin:0px; max-height:none; max-width:none; min-height:0px; min-width:0px; padding:1px 0px; position:relative; white-space:nowrap; word-spacing:normal; word-wrap:normal" class="MathJax_CHTML mjx-chtml">S=200−(x−1)(x−200)≥0⇒Smin=200

x≤y⇒x≤100" role="presentation" style="border:0px; direction:ltr; display:inline-block; float:none; font-size:16.38px; line-height:0; margin:0px; max-height:none; max-width:none; min-height:0px; min-width:0px; padding:1px 0px; position:relative; white-space:nowrap; word-spacing:normal; word-wrap:normal" class="MathJax_CHTML mjx-chtml">x≤y⇒x≤100

S=100.101−(x−100)(x−101)≤100.101⇒Smax=100.101" role="presentation" style="border:0px; direction:ltr; display:inline-block; float:none; font-size:16.38px; line-height:0; margin:0px; max-height:none; max-width:none; min-height:0px; min-width:0px; padding:1px 0px; position:relative; white-space:nowrap; word-spacing:normal; word-wrap:normal" class="MathJax_CHTML mjx-chtml">S=100.101−(x−100)(x−101)≤100.101⇒Smax=100.101

x=99 nên x+1=100

A=x^5-x^4(x+1)+x^3(x+1)-x^2(x+1)+x(x+1)-9

=x^5-x^5-x^4+x^4+...+x^2+x-9

=x-9

=90

D taị x=1/3

C = ( -5x + 4 )( 3x - 2 ) + ( -2x + 3 )( x - 2 )

C = -5x( 3x - 2 ) + 4( 3x - 2 ) - 2x( x - 2 ) + 3( x - 2 )

C = -15x² + 10x + 12x - 8 - 2x² + 4x + 3x - 6

C = -17x² + 29x - 14

Với x = -2 ta có :

C = -17.(-2)² + 29.(-2) - 14 = -140

D = ( x - 5 )( -3x + 1 ) - 3( x - 2 )( 2x - 1 )

D = x( -3x + 1 ) - 5( -3x + 1 ) - 3( 2x² - 5x + 2 )

D = -3x² + x + 15x - 5 - 6x² + 15x - 6

D = -9x² + 31x - 11

Với x = 1/3 ta có :

D = -9.(1/3)² + 31.1/3 - 11 = -5/3

x = 2005

=> x + 1 = 2006

Đặt A  = x²⁰⁰⁵ - 2006x²⁰⁰⁴ + 2006x²⁰⁰³ - 2006x²⁰⁰² + .... - 2006x² + 2006x - 1 

= x²⁰⁰⁵ - (x + 1)x²⁰⁰⁴ + (x + 1)x²⁰⁰³ - (x + 1)x²⁰⁰² + .... - (x + 1)x² + (x + 1)x - 1

= x²⁰⁰⁵ - x²⁰⁰⁵ - x²⁰⁰⁴ + x²⁰⁰⁴ + x²⁰⁰³ - x²⁰⁰³ - x²⁰⁰² + ... - x³ - x² + x² + x - 1 

= x - 1

= 2005 - 1 = 2004 

Vậy A = 2004

Với x = 20040, ta có: A = 10/20040 = 1/2004.

Vậy A = 1/2004 khi x = 20040.

-200 nha bạn

olm duyệt nha

= 200-200-200=0

-200nha bạn 

Ta có: \(3x^3-2y^3-6x^2y^2+xy\)

\(=\left(3x^3-6x^2y^2\right)+\left(xy-2y^3\right)\)

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

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

\(=\left(\dfrac{2}{3}-2\cdot\dfrac{1}{4}\right)\cdot\left(3\cdot\dfrac{4}{9}+\dfrac{1}{2}\right)\)

\(=\left(\dfrac{2}{3}-\dfrac{1}{2}\right)\cdot\left(\dfrac{4}{3}+\dfrac{1}{2}\right)\)

\(=\dfrac{1}{6}\cdot\dfrac{11}{6}=\dfrac{11}{36}\)

\(x^2+y^2-20x-2y+101=0\)

\(\Leftrightarrow\left(x-10\right)^2+\left(y-1\right)^2=0\)

\(\Leftrightarrow\hept{\begin{cases}x=10\\y=1\end{cases}}\)

Thế vô là ra