Khai triển d) (3y – x)^2 = (3y)^2 ‒ 2.3y.x + x^2 = 9y^2 – 6xy + x^2.
d) (3y – x)2.
d) (3y – x)2 = (3y)2 ‒ 2.3y.x + x2 = 9y2 – 6xy + x2.