Question

Rút gọn

A = 15(a + 2b)² - 3(a + 2b)(a + 2b + 19) + 6(2a + 4b)(1 - a - 2b)

Answer 1

Đặt      a + 2b = x

Ta có:

\(A=15x^2-3x\left(x+19\right)+12\left(1-x\right)\)

\(=15x^2-3x^2-57x+12x-12x^2\)

\(=-45x\)

\(=-45\left(a+2b\right)\)

Answer 2

Đặt a + 2b = x

Ta có:

\(A=15x^2-3x=\left(x+19\right)+12\left(1-x\right)\)

\(=15x^2-3x^2-57x+12x-12x^2\)

\(=-45x\)

\(=-45\left(a+2b\right)\)