\(\frac{1}{2}+\frac{1}{6}+\frac{1}{12}+...+\frac{1}{90}\)
\(=\frac{1}{1\cdot2}+\frac{1}{2\cdot3}+\frac{1}{3\cdot4}+...+\frac{1}{9\cdot10}\)
\(=1-\frac{1}{2}+\frac{1}{2}-\frac{1}{3}+\frac{1}{3}-\frac{1}{4}+...+\frac{1}{9}-\frac{1}{10}\)
\(=1-\frac{1}{10}\)
\(=\frac{9}{10}\)
Chú ý : Dấu '' . '' là dấu nhân
CHÚC BN HỌC TỐT !!!! ^_^
= 1/1x2 + 1/2x3 + 1/3x4 + ...... + 1/9x10
= 1- 1/2 +1/2 -1/3+1/3-1/4+ ....... +1/9 -1/10
=1-1/10
=9/10
Mình không biết đúng không nưã
\(\frac{1}{2}+\frac{1}{6}+\frac{1}{12}+...+\frac{1}{90}\)
\(=\frac{1}{1.2}+\frac{1}{2.3}+\frac{1}{3.4}+...+\frac{1}{9.10}\)
\(=1-\frac{1}{2}+\frac{1}{2}-\frac{1}{3}+\frac{1}{3}-...+\frac{1}{9}-\frac{1}{10}\)
\(=1-\frac{1}{10}\)
\(=\frac{9}{10}\)
\(\frac{1}{1.2}+\frac{1}{2.3}+\frac{1}{3.4}+...+\frac{1}{9.10}\)
=\(\frac{1}{1}.\left(\frac{1}{1}-\frac{1}{2}+...+\frac{1}{9}-\frac{1}{10}\right)\)
=\(\frac{1}{1}.\left(\frac{1}{1}-\frac{1}{10}\right)\)
=\(\frac{9}{10}\)
1/2 + 1/6 + 1/12 + ... + 1/90
= 1/1x2 + 1/2x3 + 1/3x4 + ... + 1/9x10
=1 -1/2 + 1/2 - 1/3 + 1/3 - 1/4 + ... + 1/9 - 1/10
= 1 - 1/10 = 9/10
\(=\frac{1}{1.2}+\frac{1}{2.3}+\frac{1}{3.4}+......+\frac{1}{9.10}=1-\frac{1}{10}=\frac{9}{10}\)
Mk xin pó 2 tay 2 chân lun.
Các bạn khác nếu mà biết thì hãy trả lời giúp bạn hikari joid nhé
\(A=\frac{1}{2}+\frac{1}{6}+\frac{1}{12}+...+\frac{1}{90}\)
\(A=\frac{1}{1.2}+\frac{1}{2.3}+\frac{1}{3.4}+...+\frac{1}{9.10}\)
\(A=1-\frac{1}{2}+\frac{1}{2}-\frac{1}{3}+\frac{1}{3}-\frac{1}{4}+...+\frac{1}{9}-\frac{1}{10}\)
\(A=1-\frac{1}{10}\)
\(A=\frac{9}{10}\)
Vậy phân số cần tìm là \(\frac{9}{10}\)
1/2+1/6+1/12+...+1/90
=1/1.2+1/2.3+1/3.4+...+1/9.10
=1-1/2+1/2-1/3+1/3-1/4+...+1/9-1/10
=1-1/10
=9/10
