Question

tìm x:

a)(3x-5)(7-5x+(5x+2)(3x-2)-2=0

b)x(x+1)(x+6)-x^3=5x

Answer 1

tìm x:

a) (3x - 5)(7 - 5x) + (5x + 2)(3x - 2) - 2 = 0

<=> 21x - 15x² - 35 + 25x + 15x² - 10x + 6x - 4 - 2 = 0

<=> 42x - 41 = 0

<=> 42x = 41

\(\Leftrightarrow x=\dfrac{41}{42}\)

b) x(x + 1)(x + 6) - x³ = 5x

<=> (x² + x)(x + 6) - x³ - 5x = 0

<=> x³ + 6x² + x² + 6x - x³ - 5x = 0

<=> 7x² + x = 0

<=> x(7x + 1) = 0

\(\Leftrightarrow\left[{}\begin{matrix}x=0\\7x+1=0\end{matrix}\right.\Leftrightarrow\left[{}\begin{matrix}x=0\\x=\dfrac{-1}{7}\end{matrix}\right.\)