Réponse:
1)
C=[tex](4x-8)^{2}[/tex]+(3x+8)(5x-9)
=4x * 4x - 8x*(-8x) + 3x*5x + 3x * (-9) +8*5x +8* (-9)
=[tex]16x^{2}[/tex]+64+15[tex]x^{2}[/tex]-27x+40x-72
=31[tex]x^{2}[/tex]+13x-8
2)
Quand x = 0 :
C=31 * 0² +13*0-8
=0+13*0-8
=0+0-8
= -8
Quand x = -3:
C= 31*(-3)²+13*(-3)-8
= 31*9+13*(-3)-8
= 279+13*(-3)-8
= 279-39-8
=232
Quand x = 2/3
C= 31 * (2/3)² +13* (2/3) -8
=31* ( 4/9)+13*(2/3)-8
= 124/9+13*(2/3)-8
= 124/9+26/3-8
= 124/9+78/9-8
= 202/9-72/9
=130/9
Voilà.
