Question

Rút gọn: (a + 2b - 3c - d)(a + 2b + 3c + d)

Answer 1

\(\left(a+2b-3c-d\right)\left(a+2b+3c+d\right)\)

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

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

\(=a^2+4ab+4b^2-9c^2+6cd-d^2\)

Answer 2

a, \(\left(a+2b-3c-d\right)\left(a+2b+3c+d\right)\)

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

\(=\left(a+2b\right)^2-\left(3c-d\right)^2=a^2+4ab-9c^2+6cd-d^2\)