Tìm x biết ( x^2 - x + 1 ) . ( x + 1 ) - x^3 + 3x = 15

a)  \(\left(x^2-x+1\right)\cdot\left(x+1\right)-x^3+3x=15\)

\(x^3-x^2+x+x^2-x+1-x^3+3x=15\)

\(3x+1=15\)

\(x=\frac{14}{3}\)

b) \(\left(x+3\right)\left(x-2\right)+3x=4\left(x+\frac{3}{4}\right)\)

\(x^2+3x-2x-6+3x=4x+3\)

\(x^2=9\)

\(x=+-3\)

c) \(\left(x^2-5\right)\left(x+2\right)+5x=2x^2+17\)

\(x^3-5x+2x^2-10+5x=2x^2+17\)

\(x^3=27\)

\(x=3\)