Question

tính giá trị bt : 

B=x¹⁵-8x¹⁴+8x¹³-8x¹²+...-8x²+8x-5   với x=7

Answer 1

Từ \(x=7\Rightarrow x+1=8\) thay vào B ta được :

\(B=x^{15}-\left(x+1\right)x^{14}+\left(x+1\right)x^{13}-\left(x+1\right)x^{12}+...-\left(x+1\right)x^2+\left(x+1\right)x-5\)

\(=x^{15}-x^{15}-x^{14}+x^{14}+......-x^3-x^2+x^2+x-5\)

\(=x-5=7-5=2\)

Vậy B = 2

Answer 2

\(B=x^{15}-8x^{14}+8x^{13}-8x^{12}+...+8x-5\)

\(=x^{15}-\left(x+1\right)x^{14}+\left(x+1\right)x^{13}-\left(x+1\right)x^{12}+...+\left(x+1\right)x-x+2\)

\(=x^{15}-x^{15}-x^{14}+x^{14}+x^{13}-x^{13}-x^{12}+...+x^2+x-x+2\)

\(=2\)

Answer 3

tao huy dz