a ; a + 1 ; a + 2 ; a + 3

Tên : Kiệt Phạm Tuấn

Gmail: daigiahopham2k3@gmail.com

Nguyễn Phạm Tuấn Anh: 20 không đúng bạn ơi.

\(A=\frac{1}{2.3}+\frac{1}{3.4}+\frac{1}{4.5}+.........+\frac{1}{99.100}\)

\(A=\frac{1}{2}-\frac{1}{3}+\frac{1}{3}-\frac{1}{4}+\frac{1}{4}-\frac{1}{5}+\frac{1}{5}+....+\frac{1}{99}-\frac{1}{100}\)

\(A=\frac{1}{2}-\frac{1}{100}\)

\(A=\frac{49}{100}\)

a) ( y-3) . ( y +3) = y . (y + 3) - 3 . (y + 3) = y² + 3y - 3y - 9 = y² - 9

b) \(\left(3n-2m\right)^3=\left(3n\right)^3-3.\left(3n\right)^2.2m+3.3n.\left(2m\right)^2-\left(2m\right)^3=27n^3-54n^2m+36nm^2-8m^3\)

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