\(\frac{1}{1.2}+\frac{1}{2.3}+...+\frac{1}{x\left(x+1\right)}=\frac{44}{45}\)
\(1-\frac{1}{2}+\frac{1}{2}-\frac{1}{3}+...+\frac{1}{x}-\frac{1}{x+1}=\frac{44}{45}\)
\(1-\frac{1}{x+1}=\frac{44}{45}\)
\(\frac{1}{x+1}=1-\frac{44}{45}\)
\(\frac{1}{x+1}=\frac{1}{45}\)
=> x + 1 = 45
x = 45 - 1
x = 44
Cho S=\(\frac{1}{1.2}\)+\(\frac{1}{1.2+2.3}\)+...+\(\frac{1}{1.2+2.3+3.4+...+n.\left(n+1\right)}\)
Chứng minh S<\(\frac{3}{4}\)
\(\frac{1}{1.2}+\frac{1}{2.3}+\frac{1}{3.4}+...+\frac{1}{2019.2020}=\frac{1}{x}\left(x\right)khác0\left(\right)\)
Tìm x, biết
\(\left(x+\frac{1}{2}\right)+\left(x+\frac{1}{2}\right)+\left(x+\frac{1}{2}\right)=1\)
\(\frac{1}{1.2}+\frac{1}{2.3}+\frac{1}{3.4}+...+\frac{1}{2.\left(x+1\right)}=\frac{99}{100}\)
Tìm số tự nhiên x,biết: \(\left(\frac{1}{1.2.3}+\frac{1}{2.3.4}+....+\frac{1}{8.9.10}\right).x=\frac{23}{45}\)
Tìm x biết: \(\left(\frac{1}{1.2}+\frac{1}{2.3}+\frac{1}{3.4}+...+\frac{1}{9.10}\right).\left(x-1\right)=x-\frac{1}{3}\)
\(\frac{1}{1.2}+\frac{1}{2.3}+...+\frac{1}{x\left(x+1\right)}=\frac{6}{7}\)
1, tìm x thuộc N biết
32+42=5x-1
2, tính tổng
S=1.2+2.3+3.4+...+99.100
S=1.2+2.3+3.4+...+99.100
giúp mình nha mình đang cần gấp,thanks mn
Bài 1: Tính nhanh
a) \(\frac{2}{3.5}\)+\(\frac{2}{5.7}\)+\(\frac{2}{7.9}\)+...+\(\frac{2}{19.21}\)
b) \(\left(1+\frac{1}{2}\right).\left(1+\frac{1}{3}\right).\left(1+\frac{1}{4}\right).....\left(1+\frac{1}{99}\right)\)
c) \(\frac{\frac{1}{2}+\frac{1}{3}+\frac{1}{4}+...+\frac{1}{100}}{\frac{1}{99}+\frac{2}{98}+\frac{3}{97}+...+\frac{98}{2}+\frac{99}{1}}\)
Bài 2. Tìm x, biết:
a) \(\frac{x-2}{20}=\frac{5}{2-x}\)
b) \(\left(\frac{x}{3}+\frac{1}{2}\right)\left(75\%-1\frac{1}{2}x\right)=0\)
Mk cảm ơn nhé. Các bn làm đc câu nào thì làm (nhất là b2)
tìm x biết \(\frac{1}{1.2}+\frac{1}{2.3}+\frac{1}{3.4}+\frac{1}{4.5}+...+\frac{1}{x.\left(x+1\right)}=\frac{2019}{2020}\)
