Question

Tính hợp lí

A=\(\frac{1}{3.7}+\frac{1}{7.11}+\frac{1}{11.15}+...+\frac{1}{107.111}\)

Answer 1

NHAN A VOI 3 RUI TU TINH

DỄ MÀ

Answer 2

4A=\(\frac{4}{3.7}+\frac{4}{7.11}+...+\frac{4}{107.111}\)

4A=\(\frac{1}{3}-\frac{1}{7}+\frac{1}{7}-\frac{1}{11}+...+\frac{1}{107}-\frac{1}{111}\)

4A=\(\frac{1}{3}-\frac{1}{111}=\frac{12}{37}\)

A=\(\frac{12}{37}:4=\frac{12}{37}.\frac{1}{4}=\frac{3}{37}\)

Answer 3

\(4A=\frac{4}{3.7}+\frac{4}{7.11}+...+\frac{4}{107.111}\)

\(4A=\frac{1}{3}-\frac{1}{7}+\frac{1}{7}-\frac{1}{11}+...+\frac{1}{107}-\frac{1}{111}\)

\(4A=\frac{1}{3}-\frac{1}{111}\)

\(4A=\frac{36}{111}\)

\(A=\frac{36}{111}\div4\)

\(A=\frac{9}{111}\)

Answer 4

4A = 4/3.7 + 4/7.11 +.....+ 4/107.111

4A = 1/3 - 1/7 + 1/7 - 1/11 +.....+ 1/107 - 1/111

4A = 1/3 - 1/111

4A = 108/333

A = 9/111