Bài 1:
ta có: x=7 => x+ 1 =8
thay vào biểu thức B
\(\Rightarrow B=x^{15}-\left(x+1\right)x^{14}+\left(x+1\right)x^{13}-\left(x+1\right)x^{12}+...-\left(x+1\right)x^2+\left(x+1\right)x-5\) \(B=x^{15}-x^{15}-x^{14}+x^{14}+x^{13}-x^{13}-x^{12}+...-x^3-x^2+x^2+x-5\)
\(B=x-5\)
\(B=7-5\)
\(B=2\)
Bài 2:
bn tham khảo link dưới nha:
https://olm.vn/hoi-dap/question/982834.html
Bài 3: Bn xem lại giúp mk nha!!! ( Chỗ nếu: thì....)
\(B=x^{15}-8x^{14}+8x^{13}-8x^{12}+...+8x-5\)
\(=x^{15}-\left(x+1\right)x^{14}+\left(x+1\right)x^{13}-\left(x+1\right)x^{12}+...+\left(x+1\right)x-x+2\)
\(=x^{15}-x^{15}-x^{14}+x^{14}+x^{13}-x^{13}-x^{12}+...+x^2+x-x+2\)
\(=2\)