Để B<-1 thì x+5<2

=>x<-3

\(B< -1\\ \Leftrightarrow\dfrac{x+5}{-2}< -1\\ \Rightarrow x+5>2\\ \Rightarrow x>-3\)

1) \(206^2-36=206^2-6^2=\left(206-6\right)\left(206+6\right)\)

\(=200.212=42400\)

2) \(\left(x-4\right)^2.2-\left(12x+x^2\right).2=6\)

\(\Rightarrow x^2-16x+32-24x-2x^2=6\)

\(\Rightarrow40x=26\Rightarrow x=\dfrac{13}{20}\)

\(\Leftrightarrow\left[3x+3-2x-6\right]^3+\left[2x+6-x+5\right]^3+\left[x-5-3x-3\right]^3=0\)

=>(x-3)^3+(x+11)^3+(-2x-8)^3=0

Đặt x-3=a; x+11=b

=>a^3+b^3-(a+b)^3=0

=>3ab(a+b)=0

=>(x-3)(x+11)(2x+8)=0

hay \(x\in\left\{3;-11;-4\right\}\)

a. x:(1/2+2/3)=6/5

=>x:7/6=6/5

=>x=6/5*7/6=>x=7/5

b.(x-1/2)-5(x-2/3)=3/2x

=>x-1/2-5x+10/3=3/2x

=>-4x+17/6=3/2x

=>17/6x=3/2x--4x

=>17/6=x(3/2+4)=>17/6=11/2x=>x=17/33

c.-5(x+1/5)-1/2(x-2/3)=x

=>-5x-1-1/2x+1/3=x=>-11/2x-2/3=x

=>-2/3=x+11/2x=>-2/3=x(1+11/2)=>-2/3=13/2x

=>x=-4/39

a) x : (1/2 + 2/3) = 6/5

=> x : 7/6 = 6/5

=> x = 6/5 x 7/6

      x = 7/5

b) , c) ko bít hihi

a) \(x:\left(\frac{1}{2}+\frac{2}{3}\right)=\frac{6}{5}\)

\(x:\frac{7}{6}=\frac{6}{5}\)

x=6/5 . 7/6=7/5

b)\(\left(x-\frac{1}{2}\right)-5\left(x-\frac{2}{3}\right)=\frac{3}{2}x\)

\(x-\frac{1}{2}-5x+5.\frac{2}{3}=\frac{3}{2}x\)

\(x-5x-\frac{3}{2}x=\frac{1}{2}-\frac{10}{3}\)

x(1-5-3/2)=-17/6

x. -11/2=-17/6

x=17/33 ( tự làm phép chia nha)

c) mình ghi bài làm luôn

-5x+ (-5).1/5-1/2x+1/2.2/3=x

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

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

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

-2/3=x.13/2

x=-2/3: 13/2

x= -4/39

Mấy bài này y hệt trong đề cương của mình