Question

Bài 1 : Tìm x, biết :

a) 3x(x² -2) + x²(1 - 2x) - x² = =12

b) 4x(x - 1) - 3(x² + 5) - x² = (x - 3) - (x - 4)

c) (3x - 1)(2x + 7) - (x + 1)(6x - 5) = (x + 2) - (x - 5)

d) xy(x + y) - (x + y)(x² + y² + 2xy) + y³ = 27

Giúp mình với

Answer 1

a)\(3x\left(x^2-2\right)+x^2\left(1-2x\right)-x^2=0\)

\(\Leftrightarrow x\left(3x^2-6+x-2x^2-x\right)=0\)

\(\Leftrightarrow x\left(x^2-6\right)=0\)

\(\Rightarrow\left\{{}\begin{matrix}x=0\\x^2-6=0\end{matrix}\right.\Rightarrow\left\{{}\begin{matrix}x=0\\x=\sqrt{6}\end{matrix}\right.\)

b)\(4x\left(x-1\right)-3\left(x^2+5\right)-x^2=0\)

\(\Leftrightarrow4x^2-4x-3x^2-15-x^2=0\)

\(\Leftrightarrow-4x-15=0\)

\(\Rightarrow4x=15\)

\(\Rightarrow x=\dfrac{15}{4}=3,75\)

c)\(\left(3x-1\right)\left(2x+7\right)-\left(x+1\right)\left(6x-5\right)=\left(x+2\right)-\left(x-5\right)\)

\(\Leftrightarrow6x^2+21x-2x-7-6x^2+5x-6x+5=7\)

\(\Leftrightarrow18x=9\)

\(\Rightarrow x=\dfrac{1}{2}\)