a) x^2 - 16 = (x-4)(x+4)

b) 9x^2 - 16y^2 = (3x)^2-(4y)^2 = (3x-4y)(3x+3y)

Viết tổng sau dướt dạng tích

a) x^2 - 16
= x^2 - 4^2
= ( x - 4) . ( x + 4)

b) 9x^2 - 16y^2
= ( 3x)^2 - ( 4y)^2
= ( 3x - 4y) ( 3x + 4y)

a) x^2 - 16 = (x-4)(x+4)
b) 9x^2 - 16y^2 = (3x)^2-(4y)^2 = (3x-4y)(3x+3y)