Question

chứng minh rằng

\(\frac{1}{3}-\frac{2}{3^2}+\frac{3}{3^3}-\frac{4}{3^4}+.....+\frac{99}{3^{99}}-\frac{100}{3^{100}}<\frac{3}{16}\)

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 các số a,b,c,d thuộc n biết

\(\frac{30}{43}=\frac{1}{a+\frac{1}{b+\frac{1}{c+\frac{1}{d}}}}\)

mình cho 5 tick nhoa

Answer 1

c) a=1;b=2;c=3;d=4

Answer 2

\(\frac{1}{2}\left(\frac{1}{1.2}-\frac{1}{2.3}+\frac{1}{2.3}-\frac{1}{3.4}+...+\frac{1}{8.9}-\frac{1}{9.10}\right)x=\frac{23}{45}\)

hay \(\frac{1}{2}\left(\frac{1}{1.2}-\frac{1}{9.10}\right)x=\frac{23}{45}\)

Vậy \(x=\frac{23}{11}\)

Answer 3

mơn a nèk