on considère l'expression E= (x-3)²+(x-3)(x+3) 1. Développer et réduire E. 2.Factoriser E. 3.Calculer E pour x=5.

1/E=x^2-6x+9+x^2-9 
E= 2x^2-6x
2/ E= 2x(x-3) 
3/ E= 25-30+9+25-9 
E= 20

1) E = (x-3)(x-3) + (x-3)(x+3)
E = x*x-x*3-3*x+3*3+x*x+x*3-3*x-3*3
E = 2x-3x-3x+9+2x+3x-3x-9
E = 2x+2x+3x-3x-3x-3x+9-9
E = 4x-3x-3x
E = x-3x
E = -2x

2) E = (x-3)(x-3) + (x-3)(x+3)
E = (x-3)[(x-3) + (x+3)]
E = (x-3)(x-3+x+3)
E = (x-3)(x+x-3+3)
E = (x-3)2x
E = x*2x-3*2x
E = 2x²-6x

3) E = 2x²-6x
E = 2(5*5)-6*5
E = 2*25-30
E = 50-30
E = 20