Question

Điền vào dấu 3 chấm

(a + b)³ - (a - b)³ = [(a + b) - (.........)] [(a + b)² +...............]

= 2b (..........................)

= 2b (3a² + b²)

Answer 1

\(=\left(a+b\right)^3-\left(a-b\right)^3=\left[\left(a+b\right)-\left(a-b\right)\right]\left[\left(a+b\right)^2+\left(a+b\right)\left(a-b\right)+\left(a-b\right)^2\right]\)

\(=2b\left(2a^2+2b^2+a^2-b^2\right)=2b\left(3a^2+b^2\right)\)