Môn Toán Lớp 8: 2x(x-7)=5x-35
x ³ – 2x ²-x+2=0
x ³-1/8=0
x ²-6x+8=0
25-(3-x) ²=0
Môn Toán Lớp 8: 2x(x-7)=5x-35 x ³ – 2x ²-x+2=0 x ³-1/8=0 x ²-6x+8=0 25-(3-x) ²=0
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Answer1) 2x . (x – 7) = 5x – 35<=> 2x . (x – 7) – 5x + 35 = 0<=> 2x . (x – 7) – 5 . (x – 7) = 0<=> (x – 7) . (2x – 5) = 0<=> $\left[\begin{matrix} x – 7 = 0\\2x – 5 = 0\end{matrix}\right.$<=> $\left[\begin{matrix} x = 7\\2x = 5\end{matrix}\right.$<=> $\left[\begin{matrix} x = 7\\x = \dfrac{5}{2}\end{matrix}\right.$Vậy S = {7 ; 5/2}.2) x^3 – 2x^2 – x + 2 = 0<=> (x^3 – x) – (2x^2 – 2) = 0<=> x . (x^2 – 1) – 2 . (x^2 – 1) = 0<=> (x^2 – 1) . (x – 2) = 0<=> (x – 1) . (x + 1) . (x – 2) = 0<=> $\left[\begin{matrix} x – 1 = 0\\x + 1 = 0\\x – 2 = 0\end{matrix}\right.$<=> $\left[\begin{matrix} x = 1\\x = -1\\x = 2\end{matrix}\right.$Vậy S = {1 ; -1 ; 2}.3) x^3 – 1/8 = 0<=> x^3 = 0 + 1/8<=> x^3 = 1/8<=> x^3 = (1/2)^3<=> x = 1/2Vậy S = {1/2}.4) x^2 – 6x + 8 = 0<=> (x^2 – 6x + 9) – 1 = 0<=> (x – 3)^2 – 1 = 0<=> (x – 3 – 1) . (x – 3 + 1) = 0<=> (x – 4) . (x – 2) = 0<=> $\left[\begin{matrix} x – 4 = 0\\x – 2 = 0\end{matrix}\right.$<=> $\left[\begin{matrix} x = 4\\x = 2\end{matrix}\right.$Vậy S = {2 ; 4}.5) 25 – (3 – x)^2 = 0<=> 5^2 – (3 – x)^2 = 0<=> (5 – 3 + x) . (5 + 3 – x) = 0<=> (x + 2) . (8 – x) = 0<=> $\left[\begin{matrix} x + 2 = 0\\8 – x = 0\end{matrix}\right.$<=> $\left[\begin{matrix} x = -2\\x = 8\end{matrix}\right.$Vậy S = {8 ; -2}.
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????????????????????????????????????????????????????a,2x(x-7)=5x-35<=> 2x(x-7)-5(x-7)=0<=> (x-7)(2x-5)=0<=> \(\left[ \begin{array}{l}x-7=0\\2x-5=0\end{array} \right.\)<=> \(\left[ \begin{array}{l}x=7\\x=5/2\end{array} \right.\)Vậy x=7 hoặc x=5/2b,x^3-2x^2-x+2=0<=> x^2(x-2)-(x-2)=0<=> (x-2)(x^2-1)=0<=> (x-2)(x-1)(x+1)=0<=> \(\left[ \begin{array}{l}x-2=0\\x-1=0\\x+1=0\end{array} \right.\)<=> \(\left[ \begin{array}{l}x=2\\x=1\\x=-1\end{array} \right.\)Vậy x ∈ {2;-1;1}c,x^3-1/8=0<=> x^3=1/8<=> x^3=(1/2)^3<=> x=1/2Vậy x=1/2d,x^2-6x+8=0<=> x^2-2x-4x+8=0<=> x(x-2)-4(x-2)=0<=> (x-2)(x-4)=0<=> \(\left[ \begin{array}{l}x-2=0\\x-4=0\end{array} \right.\)<=> \(\left[ \begin{array}{l}x=2\\x=4\end{array} \right.\)Vậy x=2 hoặc x=4e,25-(3-x)^2=0<=> (3-x)^2=25<=> (3-x)^2=5^2TH1: 3-x=5<=> x=-2TH2: 3-x=-5<=> x=8Vậy x=-2 hoặc x=8
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