B = x15 - 8x14 + 8x13 - 8x2 + ... - 8x2 + 8x - 5
B = x^15 - 7x^14 -x^14+7x^13+x^13-7x^12-...-x^2+7x+x-5
B = x^14(x-7) - x^14(x-7) +...+x^2(x-7)-x(x-7)+x-5
B = 7-5=2
`B = x^15 - 7x^14 - x^14 + 7x^13 + x^13 - .... +7x + x - 7 + 2`
`<=> x^14(x-7) - x^13(x-7) + ... + x - 7 + 2`
`<=> (x^14-x^13 + ... + 1)(x-7) + 2`
Thay `x = 7 <=> (x^14 - x^13 + ... + 1) xx 0 + 2 = 2`.
B = \(x^{15}-8x^{14}+8x^{13}+8x^2+...-8x^2+8x-5\)
B = \(x^{15}-7x^{14}+x^{14}+7x^{13}+x^{13}+7x^{12}-...-x^2+7x+x-5\)
B = \(x^{14}\left(x-7\right)-x^{14}\left(x-7\right)+...+x^2\left(x-7\right)-x\left(x-7\right)-5\)
B = \(7-5=2\)