a) \(x^7+x^5+1\)

\(=x^7-x+x^5-x^2+x^2+x+1\)

\(=x\left(x^6-1\right)+x^2\left(x^3-1\right)+\left(x^2+x+1\right)\)

\(=x\left(x^3+1\right)\left(x^3-1\right)+x^2\left(x-1\right)\left(x^2+x+1\right)+\left(x^2+x+1\right)\)

\(=x\left(x^3+1\right)\left(x-1\right)\left(x^2+x+1\right)+x^2\left(x-1\right)\left(x^2+x+1\right)+\left(x^2+x+1\right)\)]

\(=\left(x^2+x+1\right)\left[x\left(x^3+1\right)\left(x-1\right)+x^2\left(x-1\right)+1\right]\)

\(=\left(x^2+x+1\right)\left[x\left(x^4-x^3+x-1\right)+x^3-x^2+1\right]\)

\(=\left(x^2+x+1\right)\left(x^5-x^4+x^2-x+x^3-x^2+1\right)\)

\(=\left(x^2+x+1\right)\left(x^5-x^4+x^3-x+1\right)\)

b) \(x^5-x^4-1\)

\(=x^5-x^4+x^3-x^3+x^2-x-x^2+x-1\)

\(=x^3\left(x^2-x+1\right)-x\left(x^2-x+1\right)-\left(x^2-x+1\right)\)

\(=\left(x^2-x+1\right)\left(x^3-x-1\right)\)

b=2 nha'

hok tốt nha

k nha

ok ok 

Answer:

\(B=x^{15}-8x^{14}+8x^{13}-8x^{12}+...-8x^2+8x-5\)

Có: \(x=7\)

\(\Rightarrow8=x+1\)

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

\(B=x^{15}-x^{15}-x^{14}+x^{14}+x^{13}-x^{13}+x^{12}+...-x^3-x^2+x^2+x-5\)

\(B=\left(x^{15}-x^{15}\right)+\left(-x^{14}+x^{14}\right)+\left(x^{13}+x^{13}\right)+\left(-x^{12}+x^{12}\right)+...+\left(x^3-x^3\right)+\left(-x^2+x^2\right)+x-5\)

\(B=x-5\)

Thay vào được

\(B=7-5=2\)

em 

lớp 6

not

lớp 8

hết

HT

Toán nâng cao của lớp 6 có cái này nè , em có làm một bài nhưng mà không biết làm bài này ==" thông cẻm . Nhục cái mặt quá :)

Answer:

\(\frac{x+1}{64}+\frac{x+2}{63}+\frac{x+3}{62}+\frac{x+4}{61}=-4\)

\(\Leftrightarrow\frac{x+1}{64}+1+\frac{x+2}{63}+1+\frac{x+3}{62}+1+\frac{x+4}{61}+1=-4+4\)

\(\Leftrightarrow\frac{x+1+64}{64}+\frac{x+2+63}{63}+\frac{x+3+62}{62}+\frac{x+4+61}{61}=0\)

\(\Leftrightarrow\frac{x+65}{64}+\frac{x+65}{63}+\frac{x+65}{62}+\frac{x+65}{61}=0\)

\(\Leftrightarrow\left(x+65\right)\frac{1}{64}+\left(x+65\right)\frac{1}{63}+\left(x+65\right)\frac{1}{62}+\left(x+65\right)\frac{1}{61}=0\)

\(\Leftrightarrow\left(x+65\right)\left(\frac{1}{64}+\frac{1}{63}+\frac{1}{62}+\frac{1}{61}\right)=0\)

\(\Leftrightarrow x+65=0\)

\(\Leftrightarrow x=-65\)