a: \(A=4x^2-28x+49\)
\(=\left(2x\right)^2-2\cdot2x\cdot7+7^2\)
\(=\left(2x-7\right)^2=\left(2\cdot4-7\right)^2=1\)
b: \(B=x^3-9x^2+27x-27\)
\(=x^3-3\cdot x^2\cdot3+3\cdot x\cdot3^2-3^3\)
\(=\left(x-3\right)^3\)
\(=\left(5-3\right)^3=2^3=8\)
c: \(C=\left\lbrack\left(x-3\right)^2+\left(x+3\right)^2\right\rbrack:\left(x^2+9\right)\)
\(=\left(x^2-6x+9+x^2+6x+9\right):\left(x^2+9\right)\)
\(=\left(2x^2+18\right):\left(x^2+9\right)=2\)
=>Khi \(x=2016^{2017}\) thì C=2
d: \(D=\left(5x-11\right)^2-2\left(5x-11\right)\left(5x-9\right)+\left(5x-9\right)^2\)
\(=\left(5x-11-5x+9\right)^2\)
\(=\left(-2\right)^2=4\)
=>Khi \(x=20^{16}\) thì D=4
