Réponse:
a. 100-x²=(10-x)(10+x)
b.x²+6x+9=(x+3)²
c.36x²-25=(6x-5)(6x+5)
d.9x²-12x+4=(3x-2)²
e.49x²-49=(7x-7)(7x+7)
f.100-40+4x²=(10-2x)²
Explications:
a.10×10+10x-10x-x×x=100-x²
b.x²+2×3×x+3×3=x²+6x+9
identités remarquables :
(a-b)²=examinant+bxb=a²-2ab+b²
(a+b)²=axa+2xaxb+bxb=a²+2ab+b²
(a-b)(a+b)=axa+axb-axb+bxb=a²-b²
(faut les appliquer)
