Cho \(A=a\left(b-c\right)-b\left(a-c\right)\) và \(B=b\left(a-c\right)-a\left(b+c\right)\)

Tính tổng A + B và hiệu A - B

Tính nhanh:

\(M=\dfrac{120-\dfrac{1}{2}.40.5.\dfrac{1}{5}.20.\dfrac{1}{4}-20}{1+5+9+...+33+37+41}\)

\(N=10101.\left(\dfrac{6}{111111}+\dfrac{6}{222222}-\dfrac{7}{3.7.11.13.37}\right)\)

Tìm x:

\(\dfrac{5}{6}.|\dfrac{3}{8}-x|-\left(\dfrac{-7}{8}+\dfrac{11}{12}-\dfrac{5}{6}\right)=-\left(\dfrac{-1}{2}\right)^2\)