Réponse :
je pars du principe que ^ signifie ²
alors
M = x²- 49 <=> M = x² - 7²
<=> M = (x -7)(x +7) produit remarquable
N = 81- t² <=> N = 9² - t²
<=> N = (9 -t)(9 +t)
P =16x²- 36 <=> P = (4x)² - 6²
<=> P = (4x - 6)(4x +6)
Q =25- 4y² <=> Q = 5² - (2y)²
<=> Q = (5 - 2y)(5 +2y)