Question

Tìm x biết:

a, \(3x^2\) - ( x+2).( 3x-1)=7

b,(x+1).( \(x^2\)-x+1) = 2

c, ( x-3).( \(x^2\)+3x+9) = 37

Answer 1

a, \(3x^2-\left(x+2\right)\left(3x-1\right)=7\)

\(\Rightarrow3x^2-3x^2-x+6x-2=7\)

\(\Rightarrow5x=9\Rightarrow x=\dfrac{9}{5}\)

b, \(\left(x+1\right)\left(x^2-x+1\right)=2\)

\(\Rightarrow x^3-x^2+x+x^2-x+1=2\)

\(\Rightarrow x^3=1\)

\(\Rightarrow x=1\)

c, \(\left(x-3\right)\left(x^2+3x+9\right)=37\)

\(\Rightarrow x^3+3x^2+9x-3x^2-9x-27=37\)

\(\Rightarrow x^3=64\Rightarrow x^3=4^3\)

\(\Rightarrow x=4\)

Chúc bạn học tốt!!!

Answer 2

\(3x^2-\left(x+2\right)\left(3x-1\right)=7\)

\(\Leftrightarrow3x^2-\left(3x^2-x+2x-2\right)-7=0\Leftrightarrow3x^2-3x^2-x+2-7=0\Leftrightarrow-x-5=0\Rightarrow-x=5\Rightarrow x=-5\)

\(b,\left(x+1\right)\left(x^2-x+1\right)=2\Leftrightarrow x^3+1-2=0\Rightarrow x^3=1\Rightarrow x=1\)

\(c,\left(x-3\right)\left(x^2+3x+9\right)=37\Rightarrow x^3-27-37=0\Rightarrow x^3=64\Rightarrow x=4\)