Réponse:
a/ 9a^2 - 4 = (3a)^2 - 2^2 = (3a-2)(3a+2). (identité remarquable N3: a^2_b^2 = (a-b)(a+b))
b/ x^2 + 18x + 81= x^2+2×9×x+ 9^2 = (x+9)^2. (I.R n1 : a^2 + 2ab+ b^2 = (a+b)^2)
c/ b^2 -24b+144 = b^2_ 2×b×12 + 12^2 = (b-12)^2. (I.R n2 : a^2 - 2ab+ b^2 = (a-b)^2 )
d/ 16t^2+56t+49 = (4t)^2+ 2×4t×7 + 7^2 = (4t+7)^2. ( I.R n1)
e/ t^2-1 = t^2 - 1^2 = (t-1)(t+1). (I.R n3)
f/ (x-2)^2 - 36 = (x-2)^2 - 6^2 = ((x-2)-6)((x-2)+6).
