Bài 2:

a: Ta có: \(2x+79=x+45\)

nên 2x-x=45-79

hay x=-24

b: Ta có: \(15-\left(x+7\right)=\left(x-8\right)+22\)

\(\Leftrightarrow8-x-x-14=0\)

\(\Leftrightarrow2x=22\)

hay x=11

a) \(\dfrac{9}{7}\div x=\dfrac{3}{5}\)

           \(x=\dfrac{9}{7}\div\dfrac{3}{5}\)

          \(x=\dfrac{15}{7}\)

b) \(x+\dfrac{1}{3}=\dfrac{8}{6}-\dfrac{1}{2}\)

    \(x+\dfrac{1}{3}=\dfrac{5}{6}\)

    \(x=\dfrac{5}{6}-\dfrac{1}{3}\)

   \(x=\dfrac{1}{2}\)

a) x = 3/5 x 9/7

x = 27/35

b) x+ 1/3 = 5/6

x = 5/6 - 1/3

x = 1/2

a)\(=>x=\dfrac{9}{7}:\dfrac{3}{5}=\dfrac{15}{7}\)

b)\(x=\left(\dfrac{8}{6}-\dfrac{1}{2}\right)-\dfrac{1}{3}=\dfrac{1}{2}\)

Câu 2:Đáp số là 8/17 nhé

(5/9+4/9)x8/17

=>1x8/17=8/17

Câu 1: Tìm x:

a)  2/5× x =(thiếu đề)

 8/7: x =4/5 

x=8/7:4/5

x=10/7

Câu 2: Tính bằng cách thuận tiện nhất

5/9× 8/17 + 4/9 × 8/17

=(5/9+4/9)x8/17

=1x8/17=8/17

Câu 1

\(a,\dfrac{2}{5}\times x=4\\ x=4:\dfrac{2}{5}=10\\ b,7:x=\dfrac{4}{5}\\ x=\dfrac{4}{5}\times7=\dfrac{28}{5}\) 

Câu 2

\(=\left(\dfrac{5}{9}+\dfrac{4}{9}\right)\times\dfrac{8}{17}=1\times\dfrac{8}{17}=\dfrac{8}{17}\)

Câu 1: Tìm x:

a)  2/5× x = 4

x=4 : 2/5

x=10

 8/7: x =4/5 

x=8/7:4/5

x=10/7

Câu 2: Tính bằng cách thuận tiện nhất

5/9× 8/17 + 4/9 × 8/17

=(5/9+4/9)x8/17

=1x8/17=8/17

\(5/9× 8/17 + 4/9 × 8/17 =>(5/9+4/9)×8/17 =>1 ×8/17=8/17\)

a) 89 - (73 - x) = 20

73 - x = 89 - 20 = 69

x = 73 - 69 = 4

b) 140 : (x-8) = 7

x - 8  = 140 : 7 = 2

x = 8 + 2 = 10

\(a,89-\left(73-x\right)=20\\ 73-x=69\\ x=4\\ b,140:\left(x-8\right)=7\\ x-8=20\\ x=28\)

a: x=4

b: x=28

x      = 9/3 - 5/8

x      =  57/24

x+5/8=9/3

x       -= 9/3 - 5/8

x        =  57/24

\(x+\dfrac{5}{8}=\dfrac{9}{3}\)

\(x=\dfrac{9}{3}-\dfrac{5}{8}=\dfrac{19}{8}\)

a) (x + 3)^2 - 4x - 12 = 0

<=> (x + 3)^2 - 4(x + 3) = 0

<=> (x + 3)(x - 1) = 0

<=> x = -3 hoặc x = 1

b) x(x + 5)(x- 5) - (x - 3)(x^2 + 3x + 9) = 7

<=> x^3 - 25x - x^3 + 27 = 7

<=> -25x + 27 = 7

<=> x = 4/5

a/ \(\left(x+3\right)^2-4x-12=0\)

\(\left(x+3\right)^2-4\left(x+3\right)=0\)

\(\left(x+3\right)\left(x+3-4\right)=0\)

\(\left[{}\begin{matrix}x+3=0\Rightarrow x=-3\\x+3-4=0\Rightarrow x=1\end{matrix}\right.\)

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b/ \(x\left(x+5\right)\left(x-5\right)-\left(x-3\right)\left(x^2+3x+9\right)=7\)

\(x\left(x^2-25\right)-\left(x^3-27\right)=7\)

\(x^3-25x-x^3+27=7\)

\(-25x=-20\)

\(x=\dfrac{20}{25}=\dfrac{4}{5}\)

a, <=>x² +6x+9-4x-12=0

<=> x² +2x -3=0

<=> x² +3x -x-3=0

<=> x.(x+3) - (x+3) =0

<=> (x-1)(x+3)=0

<=> x=1 hoặc x=-3

b, <=> x(x² -25) - (x-3)(x+3)² -7=0 

<=> x³ -25x + (9-x²) (x+3) -7=0

<=> x³ -25x+ 9x+27-x³ -3x² -7=0

<=> -3x² -16x +20=0

<=>(3x-10)(x-2) =0 (đoạn này tự phân tích nha ^ ^)

<=> x= 10/3 hoặc x=2

Chúc bạn học tốt nha!