a, xem lại đè câu a hộ!
b, => ( x+ 4y)2 - 9
<=> ( x+ 4y -3)( x +4y+3)
c, => a2 + 8a + 16 - b2 -8b -16
<=> (a + 4)2 - (b + 4)2
<=> (a+4- b-4)(a+4+b+4)
<=> ( a -b)(a+b+8)
d, 36x4 - 13x2 +1
<=>(36x^4 - 12x^2 +1)- x^2
<=> ( 6x^2 -1)2 - x^2
<=> (5x^2 -1) (7x^2-1)