Đặt \(a=2009\)
\(B=\sqrt{\dfrac{\left(a-1\right)a\left(a+1\right)\left(a+2\right)\left[\left(a-1\right)^2+\left(a+2\right)\left(a-1\right)+a+1\right]}{\left[\left(a-2\right)\left(a+2\right)-\left(a-4\right)\right]\left[\left(a-2\right)\left(a-7\right)+12\left(a-1\right)\right].a.2a}}\)
\(=\sqrt{\dfrac{\left(a-1\right)\left(a+1\right)\left(a+2\right).2a^2}{\left(a^2-a\right)\left(a^2+3a+2\right).2a}}=\sqrt{\dfrac{\left(a-1\right)\left(a+1\right)\left(a+2\right).2a^2}{a\left(a-1\right)\left(a+1\right)\left(a+2\right).2a}}\)
\(=1\)