\(\text{1/1000+13/1000+25/1000+49/1000+...+87/1000+99/1000}\)
\(\text{= 1 + 13 + 25 + 37 + 49 + 51 + 63 + 75 + 87 + 99/ 1000}\)
\(\text{= ( 1 + 99 ) + ( 13 + 87) + ( 25 + 75 ) + ( 37 + 63) + ( ( 49 + 51)/ 1000}\)
\(\text{= 5 x 100/ 1000}\)
\(\text{= 500/ 1000}\)
\(\text{= 1/2 }\)
Đề bài có gì đó sai sai nên mình chữa lại nè:
\(\frac{1}{1000}+\frac{13}{1000}+\frac{25}{1000}+\frac{37}{1000}+\frac{49}{1000}+..+\frac{87}{1000}+\frac{99}{1000}\)
Ta có
\(\frac{1}{1000}+\frac{13}{1000}+\frac{25}{1000}+\frac{37}{1000}+\frac{49}{1000}+..+\frac{87}{1000}+\frac{99}{1000}\)
\(=\)\(\frac{1+13+25+37+49+...+87+99}{1000}\)
\(=\)\(\frac{\left(\left(99+1\right)\times\left(\left(99-1\right)\div12\right)+1\right)\div2}{1000}\)
\(=\)\(\frac{100\times11\div2}{1000}\)
\(=\)\(\frac{11}{10}\div2\)
\(=\)\(\frac{11\times1}{10\times2}\)
\(=\frac{11}{20}\)
Cảm ơn bạn Tuấn Phùng anh
Tuấn Phùng anh sai rồi nha
sorry mình tưởng vậy ahihi
:p