Toán Lớp 8: tìm x
a) 2x^3-50x =0
b) 9x^2-49=0
c) (2x-1)^2-25=0
d) 5x(x-3)-2x+6=0
e) x^3+5x^2-4x-20=0
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Toán Lớp 8: tìm x
a) 2x^3-50x =0
b) 9x^2-49=0
c) (2x-1)^2-25=0
d) 5x(x-3)-2x+6=0
e) x^3+5x^2-4x-20=0
Comments ( 2 )
2x(x^2-25)=0
-> \(\left[ \begin{array}{l}x=0\\x^2-25=0\end{array} \right.\)
-> \(\left[ \begin{array}{l}x=0\\x=±5\end{array} \right.\)
b) 9x^2-49=0
(3x-7)(3x+7)=0
-> \(\left[ \begin{array}{l}3x-7=0\\3x+7=0\end{array} \right.\)
-> \(\left[ \begin{array}{l}x=\frac{7}{3} \\x=-\frac{7}{3}\end{array} \right.\)
c) (2x-1)^2-25=0
(2x-1)^2=25
-> \(\left[ \begin{array}{l}2x-1=5\\2x-1=-5\end{array} \right.\)
-> \(\left[ \begin{array}{l}x=3\\x=-2\end{array} \right.\)
d) 5x(x-3)-2x+6=0
5x(x-3)-2(x-3)=0
(x-3)(5x-2)=0
-> \(\left[ \begin{array}{l}x-3=0\\5x-2=0\end{array} \right.\)
-> \(\left[ \begin{array}{l}x=3\\x=\frac{2}{5}\end{array} \right.\)
e) x^3+5x^2-4x-20=0
x^2(x+5)-4(x+5)=0
(x+5)(x^2-4)=0
(x+5)(x-2)(x+2)=0
-> x ∈ {-5;2;-2}