Question

[Phan Đức Gia Linh]

[3 câu tiếp theo nè!]

4) D = \(\dfrac{1}{25.27}\) + \(\dfrac{1}{27.29}\) + ... + \(\dfrac{1}{73.75}\)

5) E = \(\dfrac{15}{90.94}\) + \(\dfrac{15}{94.98}\) + ... + \(\dfrac{15}{146.150}\)

6) F = \(\dfrac{10}{56}\) + \(\dfrac{10}{140}\) + \(\dfrac{10}{260}\) + ... + \(\dfrac{10}{1400}\)

Các bạn cố gắng giải đầy đủ giúp mình!

Answer 1

[Carolin Ngọc]

D= 1/2. (1/25-1/27 +1/27-1/29+...+1/73-1/75)

= 1/2. (1/25 -1/75)

=1/2 . 2/75= 1/75

Answer 2

[Cuber Việt]

D = \(\dfrac{1}{25.27}+\dfrac{1}{27.29}+...+\dfrac{1}{73.75}\)

2D = 2( \(\dfrac{1}{25.27}+\dfrac{1}{27.29}+...+\dfrac{1}{73.75}\) )

= \(\dfrac{2}{25.27}+\dfrac{2}{27.29}+...+\dfrac{2}{73.75}\)

= \(\dfrac{1}{25}-\dfrac{1}{27}+\dfrac{1}{27}-\dfrac{1}{29}+...+\dfrac{1}{73}-\dfrac{1}{75}\)

= \(\dfrac{1}{25}-\dfrac{1}{75}\)

= \(\dfrac{2}{75}\)