Bonjour,
A = (5 – 2 x)² – (5–2 x)
a/ Développer et réduire l'expression A
A = (5 – 2 x)² – (5–2 x)
A = (5 – 2 x)(5 – 2 x) – (5–2 x)
A= 25-10x-10x+4x²-5+2x
A= 4x²-18x+20
b/ Calculer A pour x = - ½
A(-1/2)= 4(-1/2)²-18(-1/2)+20
A(-1/2)= 4(1/4)+18/2+20
A(-1/2)= 1+9+20
A(-1/2)= 30
c/ Factoriser A.
A = (5 – 2 x)(5 – 2 x) – (5–2 x)
A= (5-2x)(5-2x-1)
A= (5-2x)(-2x+4)
A= 2(5-2x)(-x+2) *** -2x+4=> 2(-x+2)
A= 2(2x-5)(x-2) **** attention changement de signe
