b1:thực hiện phép tính
1/2.1/3+1/3.1/4+...+1/8.1/9
b2:tìm x bt
1+1/3+1/6+1/10+...+1/x(x+1):2=1 và 2016/2017
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25 tháng 8 2023
2:
1: =>36x+14x=69+81=150
=>50x=150
=>x=3
2: 3^x=81
=>3^x=3^4
=>x=4
3: 3(2x+1)^2=75
=>(2x+1)^2=25
=>2x+1=5 hoặc 2x+1=-5
=>x=-3 hoặc x=2
1:
1: \(\dfrac{13\cdot17^4+4\cdot17^4}{17^3}-\dfrac{14\cdot3^3-14\cdot3^2}{9}\)
\(=\dfrac{17^4\cdot\left(13+4\right)}{17^3}-\dfrac{14\cdot3^2\left(3-1\right)}{9}\)
\(=17\cdot17-14\cdot2\)
=289-28
=261
2:
\(2^3\cdot5^2-\left[131-\left(23-2^3\right)^2\right]\)
\(=8\cdot25-131+\left(-1\right)^2\)
=69+1
=70
NN
0
TT
2
20 tháng 10 2021
1) \(-6x^4+4x^3-2x^2\)
2) \(=x^2+4x-21-x^2-4x+5=-16\)
3) \(=6x^2-4x-x^2-4x-4=5x^2-8x-4\)
4) \(=2x^3-4x^2-8x-3x^2+6x+12=2x^3-7x^2-2x+12\)
NT
0
2 tháng 5 2018
\(\frac{1}{2}.\frac{1}{3}+\frac{1}{3}.\frac{1}{4}+\frac{1}{4}.\frac{1}{5}+\frac{1}{5}.\frac{1}{6}+\frac{1}{6}.\frac{1}{7}+\frac{1}{7}.\frac{1}{8}+\frac{1}{8}.\frac{1}{9}\)
\(=\frac{1.1}{2.3}+\frac{1.1}{3.4}+\frac{1.1}{4.5}+\frac{1.1}{5.6}+\frac{1.1}{6.7}+\frac{1.1}{7.8}+\frac{1.1}{8.9}\)
\(=\frac{1}{2.3}+\frac{1}{3.4}+\frac{1}{4.5}+\frac{1}{5.6}+\frac{1}{6.7}+\frac{1}{7.8}+\frac{1}{8.9}\)
\(=\frac{1}{2}-\frac{1}{3}+\frac{1}{3}-\frac{1}{4}+\frac{1}{4}-\frac{1}{5}+\frac{1}{5}-\frac{1}{6}+\frac{1}{6}-\frac{1}{7}+\frac{1}{7}-\frac{1}{8}+\frac{1}{8}-\frac{1}{9}\)
\(=\frac{1}{2}-\frac{1}{9}\)
\(=\frac{7}{18}\)
2 tháng 5 2018
= 1/2.3+1/3.4+1/4.5+...+1/8.9
= 1/2-1/3+1/3-1/4+...+1/8-1/9
= 1/2-1/9
= 7/18
TT
1
13 tháng 10 2021
1: \(\left(x-1\right)^3-x\left(x-2\right)^2+1\)
\(=x^3-3x^2+3x-1-x^3+4x^2-4x+1\)
\(=x^2-x\)
2: \(2x\left(3x+2\right)-3x\left(2x+3\right)\)
\(=6x^2+4x-6x^2-9x\)
=-5x
DC
16 tháng 4 2022
BT1 :thực hành phép tính
4/3+-11/31+3/10-20/31-2/5 = 7/30
7/12-1/-16+3/4 = 67/48
2/11.-5/4+-9/11.5/4+ 1 và 3/4 = -1/4 * và 3/4 là sao bạn *
-9/27-25/75 = -2/3
Bài 1:
\(\frac{1}{2}.\frac{1}{3}+\frac{1}{3}.\frac{1}{4}+....+\frac{1}{8}.\frac{1}{9}\)
\(=\frac{1}{2.3}+\frac{1}{3.4}+....+\frac{1}{8.9}\)
\(=\frac{1}{2}-\frac{1}{3}+\frac{1}{3}-\frac{1}{4}+.....+\frac{1}{8}-\frac{1}{9}\)
\(=\frac{1}{2}-\frac{1}{9}=\frac{7}{18}\)
\(1+\frac{1}{3}+\frac{1}{6}+\frac{1}{10}+...+\frac{1}{x\left(x+1\right):2}=1\frac{2016}{2017}\)
\(\Rightarrow\frac{1}{2}\left(1+\frac{1}{3}+\frac{1}{6}+\frac{1}{10}+...+\frac{2}{x\left(x+1\right)}\right)=\frac{1}{2}.\frac{4033}{2017}\)
\(\Leftrightarrow\frac{1}{2}+\frac{1}{6}+\frac{1}{12}+\frac{1}{20}+...+\frac{1}{x\left(x+1\right)}=\frac{4033}{4034}\)
\(\Rightarrow\frac{1}{1.2}+\frac{1}{2.3}+\frac{1}{3.4}+\frac{1}{4.5}+...+\frac{1}{x\left(x+1\right)}=\frac{4033}{4034}\)
\(\Rightarrow1-\frac{1}{2}+\frac{1}{2}-\frac{1}{3}+\frac{1}{3}-\frac{1}{4}+\frac{1}{4}-\frac{1}{5}+...+\frac{1}{x}-\frac{1}{x+1}=\frac{4033}{4034}\)
\(\Rightarrow1-\frac{1}{x+1}=\frac{4033}{4034}\)
\(\Rightarrow\frac{1}{x+1}=1-\frac{4033}{4034}\)
\(\Rightarrow\frac{1}{x+1}=\frac{1}{4034}\)
\(\Rightarrow x+1=4034\)
\(\Rightarrow x=4034-1\)
\(\Rightarrow x=4033\)