C1. Tìm \(\frac {a}b\), biết rằng :a, \(A=\frac{1}{2}+\frac{1}{3}+\frac{1}{4}+...+\frac{1}{200}\)b, \(B=\frac{1}{199}+\frac{2}{198}+\frac{3}{197}+...+\frac{198}{2}+\frac{199}{1}\)c, \(C=\frac{1}{1\cdot2\cdot3\cdot4}+\frac{1}{2\cdot3\cdot4\cdot5}+...+\frac{1}{27\cdot28\cdot29\cdot30}\)C2. Tìm x...
Đọc tiếp
C1. Tìm \(\frac {a}b\), biết rằng :
a, \(A=\frac{1}{2}+\frac{1}{3}+\frac{1}{4}+...+\frac{1}{200}\)
b, \(B=\frac{1}{199}+\frac{2}{198}+\frac{3}{197}+...+\frac{198}{2}+\frac{199}{1}\)
c, \(C=\frac{1}{1\cdot2\cdot3\cdot4}+\frac{1}{2\cdot3\cdot4\cdot5}+...+\frac{1}{27\cdot28\cdot29\cdot30}\)
C2. Tìm x :
1. \(1+\frac{1}{3}+\frac{1}{6}+\frac{1}{10}+...+\frac{1}{\frac{x\left(x+1\right)}{2}}=1\frac{1991}{1993}\)
2. \(\frac{1}{5\times8}+\frac{1}{8\times11}+...+\frac{1}{11\times14}+...+\frac{1}{x\times(x+3)}=\frac{101}{1540}\)
Tìm số tự nhiên x,y biết :x-3=y*(x+2)