1/1.2 + 1/2.3 + 1/3.4 + ... + 1/73.74 + 1/74.75
= 1-1/2+1/2-1/3+1/3-1/4+...+1/73-1/74+1/74-1/75
= 1 - 1/75
= 74/75
Nhấn đúng cho mk nha!!!!!!!!!!!
\(\frac{1}{1.2}+\frac{1}{2.3}+\frac{1}{3.4}+...+\frac{1}{73.74}+\frac{1}{74.75}\)
\(=\frac{1}{1}-\frac{1}{2}+\frac{1}{2}-\frac{1}{3}+\frac{1}{3}-\frac{1}{4}+...+\frac{1}{73}-\frac{1}{74}+\frac{1}{74}-\frac{1}{75}\)
\(=1-\frac{1}{75}\)
\(=\frac{74}{75}\)
\(\frac{1}{1\cdot2}+\frac{1}{2\cdot3}+\frac{1}{3\cdot4}+...+\frac{1}{73\cdot74}+\frac{1}{74\cdot75}\)
\(=\frac{1}{1}-\frac{1}{2}+\frac{1}{2}-\frac{1}{3}+\frac{1}{3}-\frac{1}{4}+...+\frac{1}{73}-\frac{1}{74}+\frac{1}{74}-\frac{1}{75}\)
\(=\frac{1}{1}-\frac{1}{75}\)
\(=\frac{75}{75}-\frac{1}{75}\)
\(=\frac{74}{75}\)
