Question

1.Tính : 

a) x^3 - 3x^2 - 9x + 27

b) ( 3x - 2 )( 3x + 2 ) - ( 4 - 3x )^2 

2. Tìm x : 

( 2x + 5 )^2 - ( 1 + 2x )( 2x - 1 ) = -3

Answer 1

\(x^3-3x^2-9x+27=x^2\left(x-3\right)-9\left(x-3\right)=\left(x-3\right)\left(x^2-9\right)=\left(x-3\right)\left(x-3\right)\left(x+3\right)=\left(x-3\right)^2\left(x+3\right)\)

\(\left(3x-2\right)\left(3x+2\right)-\left(4-3x\right)^2=9x^2-4-16+24x-9x^2=24x-20=4\left(6x-5\right)\)

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

\(4x^2+20x+25-4x^2+1=-3\)

\(20x=-3-25-1\)

\(20x=-29\)

\(x=-\frac{29}{20}\)