Question

\(1+\frac{1}{3}+\frac{1}{6}+\frac{1}{10}+...+\frac{1}{x\left(x+1\right):2}=1\frac{1991}{1993}\)

Answer 1

chuyển 1 đi còn cái kia=1991/1993

nhân mỗi p/số với 1/2 rồi p/tích mẫu=2.3,3.4........x.(x+1)

lập hiệu ra rồi tính OK???

Answer 2

=2/2+2/6+2/12+...+...+2/x(x+1)=3984/1993

=2(1/1.2+1/2.3+1/3.4+...+1/x.(x+1)=3984/1993

=2(1-1/2+1/2-1/3+14-1/5+...+1/x-1/x+1=3984/1993

=2(1-1/x+1)=3984/1993

=2-2/x+1=3984/1993

2/x+1=2/1993

x+1=1003

x=1992

Answer 3

=2/2+2/6+2/12+...+...+2/x(x+1)=3984/1993

=2(1/1.2+1/2.3+1/3.4+...+1/x.(x+1)=3984/1993

=2(1-1/2+1/2-1/3+14-1/5+...+1/x-1/x+1=3984/1993

=2(1-1/x+1)=3984/1993

=2-2/x+1=3984/1993

2/x+1=2/1993

x+1=1003

x=1992