a, <=> \(\left(\dfrac{1}{4}xy-\dfrac{1}{3}\right)\left(\dfrac{1}{16}x^2y^2+\dfrac{1}{12}xy+\dfrac{1}{9}\right)\)
b, <=>\(\left(\dfrac{3}{4}x^2y-\dfrac{1}{2}\right)\left(\dfrac{9}{16}x^4y^2+\dfrac{3}{8}x^2y+\dfrac{1}{4}\right)\)
c, <=> \(\left(\sqrt{2}-x\right)\left(2+x\sqrt{2}+x^2\right)\)
tất cả là hằng đẳng thức nhé












