Cho \(f\left(x\right)=x^{2013}-2013x^{2012}+2013x^{2011}-...+2013x-1\). Tính \(f\left(2012\right)\)
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x=2012
nên x+1=2013
\(f\left(x\right)=x^{2013}-x^{2012}\left(x+1\right)+x^{2011}\left(x+1\right)-...-x^2\left(x+1\right)+x\left(x+1\right)-1\)
\(=x^{2013}-x^{2013}-x^{2012}+x^{2012}-...-x^3-x^2+x^2+x-1\)
=x-1
=2012-1=2011
f(x) = x2013 - 2013x2012 + 2013x2011 - 2013x2010 + .... + 2013x - 1
= x2013 - (2012 + 1)x2012 + (2012 + 1)x2011 - (2012 + 1)x2010 + .... + (2012 + 1)x - 1
= x2013 - (x + 1)x2012 + (x + 1)x2011 - (x + 1)x2010 + .... + (x + 1)x - 1
= x2013 - x . x2012 - 1 . x2012 + x . x2011 + 1 . x2011 - x . x2010 - 1 . x2010 + ... + x . x + 1 . x - 1
= x2013 - x2013 - x2012 + x2012 + x2011 - x2011 - x2010 + .... + x2 + x - 1
= x - 1 = 2012 - 1 = 2011
x=2012
nên x+1=2013
\(f\left(x\right)=x^{2013}-x^{2012}\left(x+1\right)+x^{2011}\left(x+1\right)-...+x\left(x+1\right)-1\)
\(=x^{2013}-x^{2013}-x^{2012}+x^{2012}+x^{2011}-...+x^2+x+1\)
=x+1=2013
Đặt \(g\left(x\right)=x^{2015}-x^{2014}+x^{2013}-...+x-1\)
Dễ thấy: \(f\left(x\right)=x^{2016}-2013\times g\left(x\right)\Rightarrow f\left(2012\right)=2012^{2016}-2013\times g\left(2012\right)\)(a)
Ta có: \(\left(x+1\right)\times g\left(x\right)=\left(x+1\right)\left(x^{2015}-x^{2014}+x^{2013}-...+x-1\right)\)
\(\Rightarrow\left(x+1\right)\times g\left(x\right)=x^{2016}-1\)
\(\Rightarrow\left(2012+1\right)\times g\left(2012\right)=2012^{2016}-1\)hay: \(2013\times g\left(2012\right)=2012^{2016}-1\)
Thay vào (a) ta có: \(f\left(2012\right)=2012^{2016}-\left(2012^{2016}-1\right)=1\).