Question

mình cần gấppppppppppppppppppppppppppp

Answer 1

a)=\(\dfrac{1}{1}-\dfrac{1}{2}+\dfrac{1}{2}-\dfrac{1}{3}+...+\dfrac{1}{64}-\dfrac{1}{65}=1-\dfrac{1}{65}=\dfrac{64}{65}\)

b)=\(2\left(\dfrac{1}{1x2}+\dfrac{1}{2x3}+...+\dfrac{1}{50x51}\right)=2\left(\dfrac{1}{1}-\dfrac{1}{2}+\dfrac{1}{2}-\dfrac{1}{3}+...+\dfrac{1}{50}-\dfrac{1}{51}\right)=2\left(1-\dfrac{1}{51}\right)=2x\dfrac{50}{51}=\dfrac{100}{51}\)

c)=\(\dfrac{1}{2}\left(\dfrac{2}{1x3}+\dfrac{2}{3x5}+...+\dfrac{2}{59x61}\right)=\dfrac{1}{2}\left(\dfrac{1}{1}-\dfrac{1}{3}+\dfrac{1}{3}-\dfrac{1}{5}+...+\dfrac{1}{59}-\dfrac{1}{61}\right)=\dfrac{1}{2}\left(1-\dfrac{1}{61}\right)=\dfrac{1}{2}x\dfrac{60}{61}=\dfrac{30}{61}\)

Answer 2