Bonsoir voilà la réponse :
a. x² = 49
<=> x²-49 = 0
<=> x²-7² = 0
<=> (x+7)(x-7) = 0
b. x² = 6
<=> x²-6 = 0
<=> x²-(√6)² = 0
<=> (x+√6)(x-√6) = 0
c. (x+1)² = 4
<=> (x-1)²-4 = 0
<=> (x-1)²-2² = 0
<=> [(x-1)+2][(x-1)-2] = 0
<=> (x-1+2)(x-1-2) = 0
<=> (x+1)(x-3) = 0
Voilà j'espère avoir pu t'aider ^^