Question

T-nh nhanh : (Dấu - là chữ y ngắn)

\(3+\frac{3}{5}+\frac{3}{25}+\frac{3}{125}+\frac{3}{625}\)

Answer 1

Đặt \(A=3+\frac{3}{5}+\frac{3}{25}+\frac{3}{125}+\frac{3}{625}\)

\(5A=15+3+\frac{3}{5}+\frac{3}{25}+\frac{3}{125}\)

\(5A-A=\left(15+3+\frac{3}{5}+\frac{3}{25}+\frac{3}{125}\right)-\left(3+\frac{3}{5}+\frac{3}{25}+\frac{3}{125}+\frac{3}{625}\right)\)

\(4A=15-\frac{3}{625}\)

\(A=\frac{15-\frac{3}{625}}{4}\)

Ủng hộ mk nha ^_-