bonjour
P(x) = 3 x ( x + 1)² - 6 x²+ ( x²+ 1) (x - 1)
1)
P(x) = 3 x ( x + 1)² - 6 x²+ ( x²+ 1) (x - 1)
=3x(x²+2x+1)-6x²+(x³-x²+x-1)
=3x³+6x²+3x-6x²+x³-x²+x-1
=4x³-x²+4x-1
=x²(4x-1)+(4x-1)
P(x)=(4x-1)(x²+1)
2) P(x)=0⇔(4x-1)(x²+1)=0
⇔4x-1=0 ou x²+1=0 (impossible )
⇔x=1/4
S={1/4}