\(\frac{2}{3}\times\frac{4}{5}-\frac{1}{3}\times\frac{4}{5}\)

\(=\frac{8}{15}-\frac{4}{15}\)

\(=\frac{4}{15}\)

k mk nha mấy bạn

= 4/5 x (2/3 - 1/3 )

= 4/5 x 1/3

= 4/15

ủa có mẫu r thì bn dựa vào mẫu mà lm

a) 3x5/4= 15/4

b) 1x2/3= 2/3

c) 3x4/5= 12/5

d) 3x1/4= 3/4 

Đề bài bảo tính hả bạn?

Ừ

\(\dfrac{2}{3}:4=\dfrac{2}{3}:\dfrac{4}{1}=\dfrac{2}{3}\) x \(\dfrac{1}{4}=\) \(\dfrac{2}{12}=\dfrac{1}{6}\)

\(\dfrac{2}{3}\) x \(4=\) \(\dfrac{2}{3}\) x \(\dfrac{4}{1}=\dfrac{8}{3}\)

bằng 23

=23 nhé bạn 

2x2x2x2+3x4-2:2x5=16+12-5=23

a: \(C\left(x\right)=A\left(x\right)+B\left(x\right)\)

\(=3x^4-4x^3+5x^2-4x-3-3x^4+4x^3-5x^2+2x+6\)

=-2x+3

b: Đặt C(x)=0

=>-2x+3=0

hay x=3/2

Sửa đề: \(a=1\cdot2^2+2\cdot3^2+3\cdot4^2+\cdots+98\cdot99^2\)

\(=2^2\left(2-1\right)+3^2\left(3-1\right)+4^2\left(4-1\right)+\cdots+99^2\left(99-1\right)\)

\(=\left(2_{}^3+3^3+\cdots+99^3\right)-\left(2^2+3^2+\cdots+99^2\right)\)

\(=\left(1^3+2^3+3^3+\cdots+99^3\right)-\left(1^2+2^2+3^2+\cdots+99^2\right)\)

\(=\left(1+2+\cdots+99\right)^2-\frac{99\cdot\left(99+1\right)\left(2\cdot99+1\right)}{6}\)

\(=\left(99\cdot\frac{100}{2}\right)^2-\frac{99\cdot100\cdot199}{6}=\left(99\cdot50\right)^2-33\cdot50\cdot199\)

\(=4950^2-328350=24174150\)

easy mà

=2.(1/1.2+1/2.3+...+1/1999.2000)

=2.(1/1-1/2+1/2-1/3+....1/1999-1/2000)

=2.(1-1/2000)

=2.1999/2000

=3998/2000=... tự rút gọn :D

2. là nhân à