1+2x3+4x5+6x7+...+98+99x100+101x102+103x104+...+998+999x1000

 tất cả các số này đều chia hết cho 2

    k mình nha

2.3chia hết cho 2

4.5chia hết cho 2

......

999.1000chia hết cho 2

suy ra 2.3+4.5+6.7+....+999.1000 chia hết cho 2

98+988+1=1087 không chia hết cho 2

vậy dãy trên ko chia hết cho 2

tự sửa lại cách trình bày nhé

a) 3x ( 4x - 2 ) - 4x ( 3x - 1 ) = 6

12 x² - 6x  - 12 x²+ 4x = 6

( 12 x² - 12 x² ) - ( 6x - 4x ) = 6

0 - 2x = 6

2x = 6

x = 3

a) 3x ( 4x - 2 ) - 4x ( 3x - 1 ) = 6

12 x² - 6x  - 12 x²+ 4x = 6

( 12 x² - 12 x² ) - ( 6x - 4x ) = 6

0 - 2x = 6

2x = 6

x = 3

a) 2(x - 1) + 3x = -22

   2x - 2 + 3x = -22

          5x - 2 = -22

               5x = -22 + 2

               5x = -20

                 x = -4

câu b như câu trên tự làm nha

a, ⇒x+ 3=0

⇒x = 0-3

vậy x = -3

b, ⇒TH1: 2 + x= 0

⇒x = 0 - 2

vậy x = -2

TH2: 7-x=0

x=7-0

x=7

vậy x ∈(-2;7)

a) (-2012).(x+3)=0

<=> x+3=0

<=> x=-3

b) \(\left(2+x\right).\left(7-x\right)=0\)

\(\Leftrightarrow\left\{{}\begin{matrix}2+x=0\\7-x=0\end{matrix}\right.\Rightarrow\left\{{}\begin{matrix}x=-2\\x=7\end{matrix}\right.\)

c) thiếu thì phải?

\(104.x.\left(6-x\right)=0\)

\(\Leftrightarrow\left\{{}\begin{matrix}x=0\\6-x=0\end{matrix}\right.\Rightarrow\left\{{}\begin{matrix}x=0\\x=6\end{matrix}\right.\)

d) \(x^2-3x=0\)

\(\Leftrightarrow x\left(x-3\right)=0\)

\(\Leftrightarrow\left\{{}\begin{matrix}x=0\\x-3=0\end{matrix}\right.\Rightarrow\left\{{}\begin{matrix}x=0\\x=3\end{matrix}\right.\)

Đề này đúng ra là tính nhé.

a. (3x-2)^2 +(3x+2)^2 + 2(9x^2) - 4 tại x= -1/3

Câu a sai đề nữa nè

Ta có:

\((3x-2)^2 + (3x+2)^2 + 2(9x^2-4) \)

\(= (9x^2 - 6x+4) + (9x^2+6x+4) + 2(9x^2 - 4)\)

\(= 2(9x^2+4) + 2(9x^2 -4) = 2.2.9x^2 \)

\(=36\cdot\dfrac{1}{9}=4\)

b. (x + y-7)^2 - 2(x+y -7)(y-6) + (y-6)^2 tại x= 101

Ta có:

\((x + y-7)^2 - 2(x+y -7)(y-6) + (y-6)^2\)

\(= [(x+y-7) - (y-6)]^2\)

\(= (x - 1)^2 \)

\(=100^2=10000\)

c.4x^2 - 20x +27 tại 52,5

Ta có:

\(4x^2 - 20x +27\)

\(=(2x)^2 -2.2x.5 + 25 + 2 \)

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

\(=100^2+2=10002\)

\(1,\Leftrightarrow7x=42\Leftrightarrow x=6\\ 2,\Leftrightarrow36-4x=4\Leftrightarrow4x=32\Leftrightarrow x=8\\ 3,\Leftrightarrow3x=35\Leftrightarrow x=\dfrac{35}{3}\\ 4,\Leftrightarrow x-12=144\Leftrightarrow x=156\\ 5,\Leftrightarrow x-14=16\Leftrightarrow x=30\\ 6,\Leftrightarrow3x-24=\dfrac{148}{73}\Leftrightarrow3x=\dfrac{1900}{73}\Leftrightarrow x=\dfrac{1900}{219}\\ 7,\Leftrightarrow33+x=45\Leftrightarrow x=12\\ 8,Sai.đề\\ 9,\Leftrightarrow\left(x+9\right):2=39\Leftrightarrow x+9=78\Leftrightarrow x=69\\ 11,\Leftrightarrow2\left(x+7\right)=38\Leftrightarrow x+7=19\Leftrightarrow x=12\\ 13,\Leftrightarrow2\left(x-51\right)=66\Leftrightarrow x-51=33\Leftrightarrow x=84\)

\(15,\Leftrightarrow x-19=9\Leftrightarrow x=28\\ 17,\Leftrightarrow\left(x-3\right):2=48\Leftrightarrow x-3=96\Leftrightarrow x=99\\ 19,\Leftrightarrow0x=46\Leftrightarrow x\in\varnothing\\ 8,Sai.đề\\ 14,\Leftrightarrow2x=209\Leftrightarrow x=\dfrac{209}{2}\\ 16,\Leftrightarrow2x+6=157\Leftrightarrow2x=151\Leftrightarrow x=\dfrac{151}{2}\\ 18,\Leftrightarrow5\left(x+4\right)=100\Leftrightarrow x+4=20\Leftrightarrow x=16\\ 20,\Leftrightarrow\left(3x-5\right)^3=27=3^3\Leftrightarrow3x-5=3\Leftrightarrow x=\dfrac{8}{3}\)

\(\dfrac{x+4}{104}+\dfrac{x+2}{102}=\dfrac{x+3}{103}+\dfrac{x+1}{101}\\ \Leftrightarrow\left(\dfrac{x+4}{104}-1\right)+\left(\dfrac{x+2}{102}-1\right)=\left(\dfrac{x+3}{103}-1\right)+\left(\dfrac{x+1}{101}-1\right)\\ \Leftrightarrow\dfrac{x-100}{104}+\dfrac{x-100}{102}-\dfrac{x-100}{103}-\dfrac{x-100}{101}=0\\ \Leftrightarrow\left(x-100\right)\left(\dfrac{1}{104}+\dfrac{1}{102}-\dfrac{1}{103}-\dfrac{1}{101}\right)=0\\ \Leftrightarrow x-100=0\left(vì.\dfrac{1}{104}+\dfrac{1}{102}-\dfrac{1}{103}-\dfrac{1}{101}\ne0\right)\\ \Leftrightarrow x=100\)

a) (x+8).(x+60) -x² =104

x²+6x+ 8x- 48 - x² =104

14x + 48 =104

14x =104 -48

14x =56

x =\(\frac{56}{14}\)

x =4

b) 6x² -( 2x-3)(3x+2)=0

6x² -(6x²+4x-9x-6)-1=0

6x²-(6x²-5x-6)-1=0

6x²-6x²+5x+6-1=0

5x+5=0

5x=-5

x=\(\frac{-5}{5}\)=-1

Vậy.....