Toán Lớp 8: a)7x(x-3) +7^ 2=63 b) x^2-x-12=0
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Toán Lớp 8: a)7x(x-3) +7^ 2=63 b) x^2-x-12=0
Comments ( 1 )
a)7x(x-3) +7^2=63
7x^2-21x+7x^2=63
7x(x-3-x)=63
7x.(-3)=63
x.(-21)=63
x=-3
b) x^2-x-12=0
x^2+3x-4x-12=0
(x^2+3x)-(4x+12)=0
x(x+3)-4(x+3)=0
(x+3)(x-4)=0
⇒\(\left[ \begin{array}{l}x+3=0\\x-4=0\end{array} \right.\)
⇒\(\left[ \begin{array}{l}x=-3\\x=4\end{array} \right.\)