Question

[Nguyễn Khánh Dương]

Tìm a , biết :

\(\left(1-\frac{1}{3}\right)\cdot\left(1-\frac{1}{6}\right)\cdot\left(1-\frac{1}{10}\right)\cdot\left(1-\frac{1}{15}\right)\cdot...\cdot\left(1-\frac{1}{780}\right)\cdot a=1\)

Giúp mk nha

Answer 1

[soyeon_Tiểu bàng giải]

\(\left(1-\frac{1}{3}\right).\left(1-\frac{1}{6}\right).\left(1-\frac{1}{10}\right).\left(1-\frac{1}{15}\right)...\left(1-\frac{1}{780}\right).a=1\)

\(\left(\frac{2}{3}.\frac{5}{6}.\frac{9}{10}.\frac{14}{15}...\frac{779}{780}\right).a=1\)

\(\left(\frac{4}{6}.\frac{10}{12}.\frac{18}{20}.\frac{28}{30}...\frac{1558}{1560}\right).a=1\)

\(\left(\frac{1.4}{2.3}.\frac{2.5}{3.4}.\frac{3.6}{4.5}.\frac{4.7}{5.6}...\frac{38.41}{39.40}\right).a=1\)

\(\left(\frac{1.2.3.4...38}{3.4.5.6..40}.\frac{4.5.6.7...41}{2.3.4.5..39}\right).a=1\)

\(\left(\frac{2}{39.40}.\frac{40.41}{2.3}\right).a=1\)

\(\frac{41}{39.3}.a=1\)

\(\frac{41}{117}.a=1\)

\(a=1:\frac{41}{117}\)

\(a=1.\frac{117}{41}=\frac{117}{41}\)

Vậy a = 117/41

Ủng hộ mk nha ^_-

Answer 2

[Nguyễn Khánh Dương]

các bn giups mk đi mai mk phải nộp bài rùi