Question

Cho đa thức f(x) = \(x^{10}-101x^9+101x^8-101x^7+...-101x+101\). Tính f(100)

Answer 1

Ta có:

\(x^{10}-\left(100+1\right)x^9+\left(100+1\right)x^8-\left(100+1\right)x^7+.....-\left(100+1\right)x+100+1\)

\(=x^{10}-100x^9-x^9+100x^8+x^8-100x^7-x^7+......-100x-x+100+1\)

Answer 2

\(f\left(x\right)=x^{10}-\left(100+1\right)x^9+\left(100+1\right)x^8-\left(100+1\right)x^7+...-\left(100+1\right)x+100+1\)

\(=x^{10}-100x^9-x^9+100x^8+x^8-100x^7-x^7+...-100x-x+100+1\)

\(=x^9\left(x-100\right)-x^8\left(x-100\right)+x^7\left(x-100\right)-...+x\left(x-100\right)-\left(x-100\right)+1\)

\(=\left(x-100\right)\left(x^9-x^8+x^7-...+x-1\right)+1\)

Ta có: \(f\left(100\right)=\left(100-100\right)\left(100^9-100^8+100^7-...+100-1\right)+1\)

\(=0+1=1\)

Vậy f(100) = 1.