\(E=\dfrac{2}{1\cdot3}+\dfrac{2}{3\cdot5}+\dfrac{2}{5\cdot7}+...+\dfrac{2}{97\cdot99}\\ =2\cdot\left(\dfrac{1}{1\cdot3}+\dfrac{1}{3\cdot5}+\dfrac{1}{5\cdot7}+...+\dfrac{1}{97\cdot99}\right)\\ =2\cdot\dfrac{1}{2}\cdot\left(1-\dfrac{1}{3}+\dfrac{1}{3}-\dfrac{1}{5}+\dfrac{1}{5}-\dfrac{1}{7}+...+\dfrac{1}{97}-\dfrac{1}{99}\right)\\ =1-\dfrac{1}{99}=\dfrac{98}{99}\)
Tinh: A= 1.3 + 3.5 + 5.7 + ...+ 97.99
tính tổng :
p= 2/1.3+2/3.5+2.5.7+....................+ 2/49.51
q= 1/1.3+1/3.5+................................... +1/19.21
1.3+3.5+5.7+...+97.99
D= 2/(1.3) + 2/(3.5) + ... + 2/(97.99)
c, C = 2/1.3 + 2/3.5 + 2/5.7 + .......+ 2/69.71+ 2/71.73
2/1.3+14/3.5+34/5.7+.......+322/17.19 =?
2/1.3+14/3.5+34/5.7+......+ 622/17.19 =?
Tính tổng: \(\frac{1}{1.3}+\frac{1}{3.5}+\frac{1}{5.7}+...+\frac{1}{97.99}\)
giúp mik vs, ai nhanh tick luôn nè:)))
1/1.3 + 1/3.5 + 1/5.7 +...+ 1/x.(x+2) = 20/41
