- Bằng \(\dfrac{5}{211}\)

gọi 1/547=a, 1/211=b ta đc:

\(2a.3b-546a.b-4ab< =>6ab-546ab-4ab=-544ab=\dfrac{-544}{547.211}\)

\(2\dfrac{1}{547}.\dfrac{3}{211}-\dfrac{546}{547}.\dfrac{1}{211}-\dfrac{4}{547.211}\)

\(=\left(2+\dfrac{1}{547}\right).3.\dfrac{1}{211}-\left(1-\dfrac{1}{547}\right).\dfrac{1}{211}-4.\dfrac{1}{547}.\dfrac{1}{211}\)

Đặt \(a=\dfrac{1}{547};b=\dfrac{1}{211}\)

Thay \(a=\dfrac{1}{547};b=\dfrac{1}{211}\) vào biểu thức trên , ta được :

\(\left(2+a\right).3b-\left(1-a\right)b-4ab\)

\(=6b+3ab-b+ab-4ab\)

\(=5b\)

\(=5.\dfrac{1}{211}\)

\(=\dfrac{5}{211}\)

Vậy g/t biểu thức trên là : \(\dfrac{5}{211}\)

x=7 nên x+1=8

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

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

=x+5

=7+5

=12

`B = x^15 - 8x^14 + 8x^13 - 8x^122 + ... - 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(x-7) - x^14(x-7) +...+x^2(x-7)-x(x-7)+x-5`

`B = 7-5=2`

a: \(M=\dfrac{631}{315}\cdot\dfrac{1}{651}-\dfrac{1}{105}\cdot\dfrac{2603}{651}-\dfrac{4}{315\cdot651}+\dfrac{4}{105}\)

\(=\dfrac{1}{315\cdot651}\cdot\left(631-4\right)-\dfrac{1}{105}\left(\dfrac{2603}{651}-4\right)\)

\(=\dfrac{1}{105}\cdot\dfrac{1}{1953}\cdot627+\dfrac{1}{105\cdot651}\)

\(=\dfrac{1}{105\cdot651}\left(\dfrac{1}{3}\cdot627+1\right)=\dfrac{1}{105\cdot651}\cdot210=\dfrac{2}{651}\)

b: \(N=\dfrac{1095}{547}\cdot\dfrac{3}{211}-\dfrac{546}{547\cdot211}-\dfrac{4}{547\cdot211}\)

\(=\dfrac{1}{547\cdot211}\left(1095\cdot3-546-4\right)\)

\(=\dfrac{1}{547\cdot211}\cdot2735=\dfrac{5}{211}\)

=>\(B=\left(2\cdot\frac{1}{547}\cdot\frac{3}{211}\right)-\left(\frac{546}{547}\cdot\frac{1}{211}\right)-\left(\frac{4}{547\cdot211}\right)\)

=>\(B=\frac{6}{547\cdot211}-\frac{546}{547\cdot211}-\frac{4}{547\cdot211}\)

=>\(B=\frac{6}{115417}-\frac{546}{115417}-\frac{4}{115417}\)

=>\(B=\frac{-544}{115417}\)