sua lai bai cua minh

Neu \(\left(x-2017\right)^2=1\\ =>x-2017=1\\ =>x=2018\)

Vay \(25=8\left(x-2017\right)^2+y^2\\ =>25=8+y^2\\ =>y^2=17\left(loai\right)\)(do x;y \(\in N\))

Vay \(x=2017;y=5\)

Ta co

\(25-y^2=8\left(x-2017\right)^2\\ =>25=8\left(x-2017\right)^2+y^2\)

Do

\(8\left(x-2017\right)^2\le25\\ =>\left(x-2017\right)^2\le\frac{25}{8}\)

\(=>\left(x-2017\right)^2\in\left\{0;1\right\}\)

Neu

\(\left(x-2017\right)^2=0\\ x-2017=0\\ x=2017\)

Vay:

\(25=8\left(x-2017\right)^2+y^2\\ =>25=y^2\\ =>y=5\)

Neu

\(\left(x-2017\right)^2=1\\ =>x-2017=1\\ =>x=2018\)

Vay:

\(25=8\left(x-2017\right)^2+y^2\\ =>25=1+y^2\\ =>y^2=24\)(loai do x;y \(\in N\))

Vay x=2017 ; y=5

Ta co \(\frac{a+x}{b+y}=\frac{a}{b}\)

=> \(b\left(a+x\right)=a\left(b+y\right)\)

\(ab+bx=ab+ay\)

=> \(bx=ay\)

=> \(\frac{a}{b}=\frac{x}{y}\)

Vay gia tri cua x,y tuy thuoc vao gia tri cua a,b

cau tra loi :

The circumference and area are both rational

D) 11 and 12

ban cung nen ve hinh de cho de hieu hon

40 cm = 0.4 m

Do bo ao cach mat nuoc 0.4 m nen khoang cach tu bo ao den anh cua no la

\(0.4\times0.4=0.8m\)

So met nguoi do cao

\(\frac{4.1-0.8}{2}=1.65m\)

Vay nguoi do cao 1.65m

Do \(n>2\)

=> \(2^n>2^2=4\) ma 4 > 3

=>\(2^n>3\)

=>\(2^n=\begin{cases}3k+1\\3k+2\end{cases}\)

Neu \(2^n=3k+2\)

=>\(2^n+1=3k+2+1=3k+3⋮3\) ( trai nguoc voi de bai )

=>\(2^n=3k+1\)

=> \(2^n-1=3k+1-1=3k⋮3\)

Vay \(2^n-1\) la hop so