Question

Viết biểu thức dưới dạng tổng hoặc hiệu các lập phương:

P=\(\left(\dfrac{3}{4}a+b^3\right)\left(-\dfrac{9}{16}a^2+\dfrac{3}{4}ab^3-b^6\right)\)

Answer 1

\(=-\left(\dfrac{3}{4}a+b^3\right)\left(\dfrac{9}{16}a^2-\dfrac{3}{4}ab^3+b^6\right)\\ =-\left(\dfrac{27}{64}a^3+b^{27}\right)\\ =-\dfrac{27}{64}a^3-b^{27}\)

Answer 2

\(P=\left(\dfrac{3}{4}a+b^3\right)\left(-\dfrac{9}{16}a^2+\dfrac{3}{4}ab^3-b^6\right)\)

\(P=-\left(\dfrac{3}{4}a+b^3\right)\left[\left(\dfrac{3}{4}a\right)^2-\dfrac{3}{4}ab^3+\left(b^3\right)^2\right]\)

\(P=-\left[\left(\dfrac{3}{4}a\right)^3+b^9\right]\)

\(P=\dfrac{-27}{64}a^3-b^9\)