Question

P(x)=x⁷- 80x⁶ + 80x⁵ - 80 x⁴ + ... + 80x + 15 voi x= 79

Answer 1

x = 79 => x+1 = 80

Thay x+1 = 80 vào P(x)=x⁷- 80x⁶ + 80x⁵ - 80 x⁴ + ... + 80x + 15, có:

P(x)=x⁷- (x+1)x⁶ + (x+1)x⁵ - (x+1) x⁴ + ... + (x+1)x + 15

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

P(x) = \(x+15\)

Thay x = 79 vào P(x) = x+15; cs:

P(x) = 79 + 15 = 94

Answer 2

\(x=79\Rightarrow80=x+1\)

\(B=x^7-\left(x+1\right)x^6+\left(x+1\right)x^5-\left(x+1\right)^4+...+\left(x+1\right)x+15\)

    \(=x^7-x^7+...+x+15=79+15=94\)