mình cũng làm vậy nhưng k chắc. cảm ơn cậu

x+20=40*1/2

x+20=20

x=20-20

x=0

Ta có:

\(A=\left(x+y\right)\left(x+2y\right)\left(x+3y\right)\left(x+4y\right)+y^4\)

\(=\left(x^2+5xy+4y^2\right)\left(x^2+5xy+6y^2\right)+y^4\)

Đặt \(t=x^2+5xy+5y^2\) ta đc:

\(A=\left(t-y^2\right)\left(t+y^2\right)+y^4\)

\(=t^2-y^4+y^4\)

\(=t^2=\left(x^2+5xy+5y^2\right)^2\)

Vì \(x,y,z\in Z\) nên \(x^2\in Z;5xy\in Z;5y^2\in Z\)

\(\Rightarrow x^2+5xy+5y^2\in Z\)

Đpcm

532/3+5/823=176+5/823=14485/823

=200

k

Write a composition (from 100 to 120 words) to talk about "Travelling is a means of education"

\(200+200=200\cdot2=400.\)

200 + 200 = 400

k nha mọi người ^_-

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