Question

@satellite73

Answer 1

\[4x-8y=0\]
\[4x=8y\]
\[x=2y\]

Answer 2

then \(x^2+y^2=25\) replace \(x\) by \(2y\) and get
\[(2y)^2+y^2=25\]

Answer 3

square and get
\[4y^2+y^2=25\] add to get \[5y^2=25\] divide by \(5\) and get \[y^2=5\] so
\[y=\pm\sqrt5\]

Answer 4

then since \(x=2y\) you have \(x=-2\sqrt5\) or \(x=2\sqrt5\)
lets check the result and see if it is right

Answer 5

http://www.wolframalpha.com/input/?i=x^2%2By^2%3D25%2C+x%3D2y
yes, it is right

Answer 6

thank you sooo much