rút gọn :A=(1+1/2)(1+1/2+1/3)...(1+1/2+...+1/10)
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![](https://rs.olm.vn/images/avt/0.png?1311)
![](https://rs.olm.vn/images/avt/0.png?1311)
1:
I2x+3I = 5
=> 2x+3 = 5 hoặc 2x+3 = -5
=> 2x = 5 - 3 hoặc 2x = -5 - 3
=> 2x = 2 hoặc 2x = -8
=> x = 2 hoặc x = -4
2:
B = 1/2.2/3.3/4.4/5.....27/28
= 1.2.3.4.5.6...27/2.3.4.5.6...28
= 1/28
3:
2A = 2(1+1/2+1/2^2+1/2^3+1/2^4+...+1/2^2015) = 2+1+1/2+1/2^2+1/2^3+...+1/2^2014
=> 2A-A = ( 2+1+1/2+1/2^2+1/2^3+...+1/2^2014)-(1+1/2+1/2^2+1/2^3+...+1/2^2015)
=> A = 2-1/2^2015
![](https://rs.olm.vn/images/avt/0.png?1311)
A=(15/10-4/10+1/10)/(18/12-8/12+1/12)
A=(6/5)/(11/12)
A=(6/5)*(12/11)
A= 72/55
minh chi biet cach tinh ra the thoi
chuc ban hoc gioi
![](https://rs.olm.vn/images/avt/0.png?1311)
\(\left(\dfrac{3}{2}-\dfrac{2}{5}+\dfrac{1}{10}\right):\left(\dfrac{3}{2}-\dfrac{2}{3}+\dfrac{1}{12}\right)\)
=\(\left(\dfrac{11}{10}+\dfrac{1}{10}\right):\left(\dfrac{5}{6}+\dfrac{1}{12}\right)\)
=\(\dfrac{6}{5}:\dfrac{11}{12}=\dfrac{72}{55}\)
![](https://rs.olm.vn/images/avt/0.png?1311)
a) 12/15 rút gọn cho 3 bằng 4/5
b) 20/15 rút gọn cho 5 bằng 4/3
c)36/24 rút gon cho 6 bằng 6/4 lại rút gọn tiếp cho 2 bằng 3/2
d) 2/4 rút gọn cho 2 bằng 1/ 2
e) 6/8 rút gọn cho 2 bằng 3/4
g) 4/10 rút gọn cho 2 bằng 2/ 5 .
Đáp án là như vậy k cho mình nha !!!
![](https://rs.olm.vn/images/avt/0.png?1311)
Ta có: \(A=\left(\sqrt{6}+\sqrt{10}\right)\cdot\sqrt{4-\sqrt{15}}\)
\(=\left(\sqrt{5}+\sqrt{3}\right)\left(\sqrt{5}-\sqrt{3}\right)\)
=5-3=2
![](https://rs.olm.vn/images/avt/0.png?1311)
![](https://rs.olm.vn/images/avt/0.png?1311)
Ta có: \(A=\dfrac{2x}{1-x^3}+\dfrac{1}{x^2-x}+\dfrac{1}{x^2+x+1}\)
\(=\dfrac{-2x}{\left(x-1\right)\left(x^2+x+1\right)}+\dfrac{1}{x\left(x-1\right)}+\dfrac{1}{x^2+x+1}\)
\(=\dfrac{-2x^2+x^2+x+1+x^2-x}{x\left(x-1\right)\left(x^2+x+1\right)}\)
\(=\dfrac{1}{x\left(x-1\right)\left(x^2+x+1\right)}\)
Thay x=10 vào A, ta được:
\(A=\dfrac{1}{10\cdot\left(10^3-1\right)}=\dfrac{1}{10\cdot999}=\dfrac{1}{9990}\)
![](https://rs.olm.vn/images/avt/0.png?1311)
a: =>(x+10)(x-1)=0
=>x=-10 hoặc x=1
b: \(A=x^3-1-\left(x+5\right)\left(x^2-3\right)-5x^2-10x-5\)
\(=x^3-5x^2-10x-6-x^3+3x-5x^2+15\)
=-7x+9
=110/13