a) x + 2x - 1 = 0

<=> 3x - 1 = 0

<=> 3x = 0 + 1

<=> 3x = 1

<=> x = 1/3

=> x = 1/3

b) f(7) = x + 2x - 1 = 7 + 2.7 - 1 = 20 

=> f(7) = 20

f(-3) = (-3) + 2.(-3) - 1 = -10

=> f(-3) = -10

c) x + 2x - 1 = 14

<=> 3x - 1 = 14

<=> 3x = 14 + 1

<=> 3x = 15

<=> x = 5

=> x = 5

bài 1/ 

a) ta có: \(A=\frac{15}{x-1}\)

Để A là phân số \(\Rightarrow x-1\ne0\)

                          \(\Rightarrow x\ne1\)

b) Nếu x = 7

\(\Rightarrow A=\frac{15}{7-1}\)

\(\Rightarrow A=\frac{15}{6}\)

Nếu x = -3

\(\Rightarrow A=\frac{15}{-3-1}\)

\(\Rightarrow A=\frac{15}{-4}\)

Nếu x = 4

\(\Rightarrow A=\frac{15}{4-1}\)

\(\Rightarrow A=\frac{15}{3}=5\)

c) Ta có: \(B=5\)

\(\Leftrightarrow A=\frac{15}{x-1}=5\)

\(\Leftrightarrow x-1=3\)

\(\Leftrightarrow x=4\)

Bài 2/

a) \(\frac{x}{3}=\frac{2}{6}\)

\(\Leftrightarrow6x=6\)

\(\Leftrightarrow x=1\)

b) \(-\frac{x}{14}=\frac{10}{-7}\)

\(\Leftrightarrow7x=140\)

\(\Leftrightarrow x=20\)

hok tốt!!

tìm giá trị x để biểu thức nguyên

D=2x-3/x+5 

E=x^2-5/x-3

Để E nguyên thì x-1 / x+3 nguyên , tức là x-1 chia hết cho x+3 hay x+3-4 chia hết cho x+3 . Từ đó suy ra -4 chia hết cho x+3 hay x+3 là ước của -4 . Còn lại bạn tự làm nha...Thanks

a) \(37-\left(x-25\right)=x+14\)

\(\Leftrightarrow\)\(37-x+25=x+14\)

\(\Leftrightarrow\)\(x+x=37+25-14\)

\(\Leftrightarrow\)\(2x=48\)

\(\Rightarrow\)\(x=\frac{48}{2}=24\)

Vậy \(x=24\)

b) \(11-\left(x-3\right)^2=0\)

\(\Leftrightarrow\)\(\left(x-3\right)^2=11-0=11\)

\(\Leftrightarrow\)\(x-3=\sqrt{11}\)

\(\Rightarrow\)\(x=\sqrt{11}+3\)

Vậy \(x=\sqrt{11}+3\)

Ta có \(P=\frac{7x-14}{x+5}=7+\frac{21}{x+5}\)

P có giá trị nguyên =>\(\frac{21}{x+5}nguyên\)

\(\Rightarrow x+5\inƯ\left(21\right)\)

\(\Rightarrow x=\left\{-26;-16;-12;-8;-6;-4;-2;2\right\}\)

ahihi

Đk: \(x\ne1;x\ne0\)

a) \(E=\dfrac{x\left(x+1\right)}{\left(x-1\right)^2}:\left[\dfrac{x+1}{x}+\dfrac{1}{x-1}+\dfrac{2-x^2}{x\left(x-1\right)}\right]\)

\(=\dfrac{x\left(x+1\right)}{\left(x-1\right)^2}:\dfrac{\left(x+1\right)\left(x-1\right)+x+2-x^2}{x\left(x-1\right)}\)

\(=\dfrac{x\left(x+1\right)}{\left(x-1\right)^2}.\dfrac{x\left(x-1\right)}{x+1}\)

\(=\dfrac{x^2}{x-1}\)

b) \(E>1\Leftrightarrow\dfrac{x^2}{x-1}>1\) \(\Leftrightarrow\dfrac{x^2-x+1}{x-1}>0\) \(\Leftrightarrow x-1>0\) 

( do \(x^2-x+1=\left(x-\dfrac{1}{2}\right)^2+\dfrac{3}{4}>0\forall x\) )

\(\Leftrightarrow x>1\)

Vậy để E>1 thì x>1

c) \(E=\dfrac{x^2}{x-1}=\dfrac{x^2-1+1}{x-1}=\dfrac{\left(x-1\right)\left(x+1\right)+1}{x-1}=x+1+\dfrac{1}{x-1}\)

\(E\in Z\Leftrightarrow x+1+\dfrac{1}{x-1}\in Z\) mà \(x\in Z\)

\(\Rightarrow x-1\inƯ\left(1\right)=\left\{-1;1\right\}\)

\(\Leftrightarrow x=0\left(ktm\right);x=2\left(tm\right)\)

Vậy \(x=2\) thì \(E\in Z\).

1) x - 3 = 19 - x \(\Rightarrow\)x + x = 19 + 3 \(\Rightarrow\)2x = 22 \(\Rightarrow\)x = 11

2)  -14 - y = 36 -( -y ) -( - 24 ) \(\Rightarrow\)-14 - y = 36 + y +24 \(\Rightarrow\)-y - y = 36 + 24 + 14 \(\Rightarrow\)-2y = 74 \(\Rightarrow\)y = -37

3)  10 - y = 4 + y \(\Rightarrow\)10 - 4 = y + y \(\Rightarrow\)6 = 2y \(\Rightarrow\)y = 3