Ta có: \(\frac{1}{\left(2n+1\right)\left(2n+3\right)}-\frac{1}{\left(2n+3\right)\left(2n+5\right)}\)

\(=\frac{2n+5-\left(2n+1\right)}{\left(2n+1\right)\left(2n+3\right)\left(2n+5\right)}\)

\(=\frac{4}{\left(2n+1\right)\left(2n+3\right)\left(2n+5\right)}\)

=>\(\frac{1}{\left(2n+1\right)\left(2n+3\right)\left(2n+5\right)}=\frac14\left(\frac{1}{\left(2n+1\right)\left(2n+3\right)}-\frac{1}{\left(2n+3\right)\left(2n+5\right)}\right)\)

Do đó, ta có:

\(\frac{1}{1\cdot3\cdot5}=\frac14\left(\frac{1}{1\cdot3}-\frac{1}{3\cdot5}\right)\)

\(\frac{1}{3\cdot5\cdot7}=\frac14\left(\frac{1}{3\cdot5}-\frac{1}{5\cdot7}\right)\)

...

\(\frac{1}{25\cdot27\cdot29}=\frac14\left(\frac{1}{25\cdot27}-\frac{1}{27\cdot29}\right)\)

Do đó: \(\frac{1}{1\cdot3\cdot5}+\frac{1}{3\cdot5\cdot7}+\cdots+\frac{1}{25\cdot27\cdot29}=\frac14\left(\frac{1}{1\cdot3}-\frac{1}{3\cdot5}+\frac{1}{3\cdot5}-\frac{1}{5\cdot7}+\cdots+\frac{1}{25\cdot27}-\frac{1}{27\cdot29}\right)\)

\(=\frac14\left(\frac{1}{1\cdot3}-\frac{1}{27\cdot29}\right)\)

=>\(36\left(\frac{1}{1\cdot3\cdot5}+\frac{1}{3\cdot5\cdot7}+\cdots+\frac{1}{25\cdot27\cdot29}\right)=36\cdot\frac14\left(\frac{1}{1\cdot3}-\frac{1}{27\cdot29}\right)\)

=>\(\frac{36}{1\cdot3\cdot5}+\frac{36}{3\cdot5\cdot7}+\cdots+\frac{36}{25\cdot27\cdot29}=9\left(\frac13-\frac{1}{27\cdot29}\right)=3-\frac{1}{3\cdot29}=\frac{3\cdot3\cdot29-1}{3\cdot29}=\frac{260}{87}\)

Trả lời :

- [ - ( 36 ) + 25 - ( -90 )] - [ -36 - 25 ]

=36 - 25 - 90 + 36 + 25

= 90

hok tốt!

-[-(36)+25-(-90]-[-36-25]=-140

# hok tốt #

Đáp án: 36 25 < 25 36 Giải thích các bước giải: 36 25 = ( 6 2 ) 25 = 6 50 25 36 = ( 5 2 ) 36 = 5 72 6 50 = ( 6 5 ) 10 Mà ( 6 5 ) 10 < ( 5 7 ) 10 < 5 72 ⇒ ( 6 5 ) 10 < 5 72 Vậy 36 25 < 25 36

25³⁶<36²⁵

^{Chúc bn học tốt}

^k mk nha

\(36.\left(\frac{1}{1}-\frac{1}{3}-\frac{1}{5}+\frac{1}{3}-\frac{1}{5}-\frac{1}{7}+...+\frac{1}{25}-\frac{1}{27}-\frac{1}{29}\right).x=\frac{4}{25}\)

Triệt tiêu còn

\(36.\left(\frac{1}{1}-\frac{1}{29}\right).x=\frac{4}{25}\)

từ đây dễ rồi, tình lần lượt rồi tìm x nhé

a. (-7).(-3).17.(-1)²

= (-7).(-3).17.1

= 21.17.1

=357.1

=357

`#3107.101107`

a)

`2/5 \sqrt{25} - 1/2 \sqrt{4}`

`= 2/5 * \sqrt{5^2} - 1/2 * \sqrt{2^2}`

`= 2/5*5 - 1/2*2`

`= 2 - 1`

`= 1`

b)

`0,5*\sqrt{0,09} + 5*\sqrt{0,81}`

`= 0,5*\sqrt{(0,3)^2} + 5*\sqrt{(0,9)^2}`

`= 0,5*0,3 + 5*0,9`

`= 0,15 + 4,5`

`= 4,65`

c)

`2/5\sqrt{25/36} - 5/2\sqrt{4/25}`

`= 2/5*\sqrt{(5^2)/(6^2)} - 5/2*\sqrt{(2^2)/(5^2)}`

`= 2/5*5/6 - 5/2*2/5`

`= 1/3 - 1`

`= -2/3`

d)

`-2 \sqrt{(-36)/(-16)} + 5 \sqrt{(-81)/(-25)}`

`= -2*\sqrt{36/16} + 5*\sqrt{81/25}`

`= -2*\sqrt{(6^2)/(4^2)} + 5*\sqrt{(9^2)/(5^2)}`

`= -2*6/4 + 5*9/5`

`= -3 + 9`

`= 6`

Xem lại kết quả câu c nhé bạn!