Question

Tính P_(x)

P_(x)=-80x⁶+80⁵-80x⁴+...+80x+15 ; x=79

giúp tôi với

 

Answer 1

x=79

nên x+1=80

\(P\left(x\right)=-80x^6+80x^5-80x^4+...+80x+15\)

\(=-x^6\left(x+1\right)+x^5\left(x+1\right)-x^4\left(x+1\right)+...+x\left(x+1\right)+15\)

\(=-x^7-x^6+x^6+x^5-x^5-x^4+...+x^2+x+15\)

\(=-x^7+x+15\)

\(=-79^7+79+15\)

\(=-79^7+94\)

Answer 2

\(x=79\Leftrightarrow x+1=80\\ \Leftrightarrow P\left(x\right)=-\left(x+1\right)x^6+\left(x+1\right)x^5-\left(x+1\right)x^4+...+\left(x+1\right)x+15\\ P\left(x\right)=-x^7-x^6+x^6+x^5-x^5-x^4+...+x^2+x+15\\ P\left(x\right)=-x^7+x+15=-79^7+94\)