(x +1) + (x + 2) + (x + 3) + (x + 100) = 7450

 100x + (1 + 2 + 3 + ... + 100)          = 7450

 100x + 5050                                  = 7450

 100x                                             = 7450 - 5050

 100x                                             = 2400

      x                                             = 2400 : 100

      x                                             = 24

sao z bn

Câu 11:

=>4,6x=6,21

=>x=1,35

12: \(A=-\left(1.4-x\right)^2-1.4< =-1.4\)

=>x=-1,4

Câu 9:

\(\Leftrightarrow\dfrac{10a+b}{100c+90+d}=\dfrac{1}{2}-\dfrac{1}{7}+\dfrac{1}{7}-\dfrac{1}{12}+...+\dfrac{1}{92}-\dfrac{1}{97}=\dfrac{1}{2}-\dfrac{1}{97}=\dfrac{95}{194}\)

=>a=9; b=5; c=1; d=4

=>a+b+c+d=9+5+1+4=19

Câu 2: 

\(C=-x+\sqrt{x}\)

\(=-\left(x-\sqrt{x}+\dfrac{1}{4}\right)+\dfrac{1}{4}\)

\(=-\left(\sqrt{x}-\dfrac{1}{2}\right)^2+\dfrac{1}{4}\le\dfrac{1}{4}\forall x\)

Dấu '=' xảy ra khi \(x=\dfrac{1}{4}\)

\(1,3x-7=19\\ \Rightarrow3x=26\\ \Rightarrow x=\dfrac{26}{3}\\ 2,\left(2x+1\right)\left(x-3\right)=0\\ \Rightarrow\left[{}\begin{matrix}2x+1=0\\x-3=0\end{matrix}\right.\\ \Rightarrow\left[{}\begin{matrix}x=-\dfrac{1}{2}\\x=3\end{matrix}\right.\\ 3,3x+\dfrac{2}{4}+1=5x-\dfrac{1}{3}\\ \Rightarrow5x-\dfrac{1}{3}-3x-\dfrac{2}{4}-1=0\\ \Rightarrow2x-\dfrac{11}{6}=0\\ \Rightarrow2x=\dfrac{11}{6}\\ \Rightarrow x=\dfrac{11}{12}\)

\(4,\dfrac{x}{15}+\dfrac{1}{2}-\dfrac{x}{50}=\dfrac{5}{6}\\ \Rightarrow\dfrac{x}{15}-\dfrac{x}{50}=\dfrac{5}{6}-\dfrac{1}{2}\\ \Rightarrow x\left(\dfrac{1}{15}-\dfrac{1}{50}\right)=\dfrac{1}{3}\\ \Rightarrow\dfrac{7}{150}x=\dfrac{1}{3}\\ \Rightarrow x=\dfrac{50}{7}\)

a/ -3x=-60+30

=> -3x=-30

=> x=(-30):(-3)

=> x=10

Ban oi phai x,y∈Z thi moi lam dc

b/x.y=7

Vi x,y∈U(7)=(1,-1,7,-7)

Với x=1 => y=7 y=1=>x=7

x=-1 =>x=-7 y=-1=>x=-7

x=7 => x=1 y=7=>x=7

x=-7 => x=-1 y=-7=>x=-1

c/(x-1)(y+2)=-7

x-1 va y+2∈U(-7)=(1,-1,7,-7)

Bạn giải giống câu b/ nhưng x,y trái đâu nhé

d/2x-3=5x-7

=>(-3)+7=5x-2x

=>4=3x

=>x=4/3

e/(-2)²-8x=20

=>4-8x=20

=>4-20=8x

=>-16=8x

=>x=-2

f/17-(-31)+3x=2x-(-50)

=>17+31+3x=2x+50

=>49+3x=2x+50

=> 3x-2x=50-49

=> x=1

g/2y²-16=34

=>2y²=34+16

=>2y²=50

=>y²=50:2

=>y²=25=5²=(-5)²

=>y=5 va y=-5

a) \(\left(-3\right)x-30=-60\)

\(\Leftrightarrow\left(-3\right)x=-60+30\)

\(\Leftrightarrow\left(-3\right)x=-30\)

\(\Leftrightarrow x=\left(-30\right):\left(-3\right)\)

\(\Leftrightarrow x=10\)

b) \(xy=7\)

\(\Rightarrow xy=1.7=7.1=\left(-1\right).\left(-7\right)=\left(-7\right).\left(-1\right)\)

Ta có bảng sau:

KL: Các cặp số (x; y)...

c) \(\left(x-1\right)\left(y+2\right)=-5\)

\(\Rightarrow\left(x-1\right)\left(y+2\right)=1.\left(-5\right)=\left(-5\right).1=\left(-1\right).5=5.\left(-1\right)\)

Ta có bảng sau:

KL: Các cặp số (x; y)...

d) \(2x-3=5x-7\)

\(\Leftrightarrow2x-5x=-7+3\)

\(\Leftrightarrow-3x=-4\)

\(\Leftrightarrow x=\dfrac{4}{3}\)

e) \(\left(-2\right)^2-8x=20\)

\(\Leftrightarrow4-8x=20\)

\(\Leftrightarrow8x=4-20\)

\(\Leftrightarrow8x=-16\)

\(\Leftrightarrow x=-2\)

f) \(17-\left(-31\right)+3x=2x-\left(-50\right)\)

\(\Leftrightarrow17+31+3x=2x+50\)

\(\Leftrightarrow48+3x=2x+50\)

\(\Leftrightarrow3x-2x=50-48\)

\(\Leftrightarrow x=2\)

g) \(2y^2-16=34\)

\(\Leftrightarrow2y^2=34+16\)

\(\Leftrightarrow2y^2=50\)

\(\Leftrightarrow y^2=50:2=25\)

\(\Leftrightarrow y^2=5^2=\left(-5\right)^2\)

\(\Leftrightarrow\left[{}\begin{matrix}y=5\\y=-5\end{matrix}\right.\)

a)

− 12 . x = − 15 . − 4 − 12 − 12 . x = 60 − 12 − 12 . x = 48                x = 48 : − 12                x = − 4

b) 

− 9 . x + 3 = − 2 . − 7 + 16 − 9 . x + 3 = 14 + 16 − 9 . x + 3 = 30 − 9 . x           = 30 − 3 − 9 . x           = 27              x           = 27 : − 9              x           = − 3

c)

− 12 . x − 34 = 2 − 12 . x               = 2 + 34 − 12 . x               = 36                x                = 36 : − 12                x                = − 3

a)

− 12 . x = − 15 . − 4 − 12 − 12 . x = 60 − 12 − 12 . x = 48                x = 48 : − 12                x = − 4

b)

− 9 . x + 3 = − 2 . − 7 + 16 − 9 . x + 3 = 14 + 16 − 9 . x + 3 = 30 − 9 . x           = 30 − 3 − 9 . x           = 27              x           = 27 : − 9              x           = − 3

c) 

− 12 . x − 34 = 2 − 12 . x               = 2 + 34 − 12 . x               = 36                x                = 36 : − 12                x                = − 3