Question

Tìm x biết :

a) \(x\left(x^2+x+1\right)-x^2\left(x-1\right)=2x+5\)

b)(x-3)(x-2)-(x+1)(x-5)=0

c)\(x\left(2x-1\right)\left(x+5\right)-\left(2x^2+1\right)\left(x+4,5\right)=3,5\)

Answer 1

a, \(x\left(x^2+x+1\right)-x^2\left(x+1\right)=2x+5\)

\(\Rightarrow x^3+x^2+x-x^3-x^2-2x=5\)

\(\Rightarrow-x=5\Rightarrow x=-5\)

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

\(\Rightarrow x^2-2x-3x+6-\left(x^2-5x+x-5\right)=0\)

\(\Rightarrow x^2-5x+6-x^2+4x+5=0\)

\(\Rightarrow-x=-5-6\Rightarrow x=11\)

c, \(x\left(2x-1\right)\left(x+5\right)-\left(2x^2+1\right)\left(x+4,5\right)=3,5\)

\(\Rightarrow x\left(2x^2+10x-x-5\right)-\left(2x^3+9x^2+x+4,5\right)=3,5\)

\(\Rightarrow2x^3+9x^2-5x-2x^3-9x^2-x-4,5=3,5\)

\(\Rightarrow-6x=3,5+4,5\Rightarrow-6x=8\Rightarrow x=-\dfrac{4}{3}\)

Chúc bạn học tốt!!!