Question

Tìm x:
a)(x+3)²-4x-12=0
b)x(x+5)(x-5)-(x-3)(x²+3x+9)=7

Answer 1

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

Answer 2

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

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

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

\(-25x=-20\)

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

Answer 3

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!

Answer 4

a, (x+3)²-4x-12=0
    x+6x+9-4x-12=0
    (x+6x-4x)+(9-12)=0
    3x-3=0
    3x=0+3
    3x=3
    x=3:3
    x=1
Vậy x=1
b, x(x+5)(x-5)-(x-3)(x²+3x+9)=7
    x(x²-5²)-(x-3)(x²+3x+3²)=7
    x³-25x-x³+3³=7
    (x³-x³)-25x+27=7
    -25x=7-27
    -25x=-20
    x=-20:(-25)
    x=0,8
Vậy x=0,8

Answer 5

a)(x+3)²-4x-12=0
   (x+3)²-4(x+3)=0
   (x+3)(x-1)=0
TH1:x+3=0\(\Rightarrow\)x=-3
TH2:x-1=0\(\Rightarrow\)x=1
b)x(x+5)(x-5)-(x-3)(x²+3x+9)=7
   x(x²-25)-x³+27=7
   x³-25x-x³=-20
           -25x=-20
               x=4/5 
 

Answer 6

a: \(\Leftrightarrow\left(x+3\right)\left(x-1\right)=0\)

\(\Leftrightarrow\left[{}\begin{matrix}x=-3\\x=1\end{matrix}\right.\)