<PRE><B>Question 529769</B>
x^2 + y^2 = 80
x = 2y

(2y)^2 + y^2 = 80
4y^2 + y^2 = 80
5y^2 = 80
y^2 = 16
y=4  [or -4]

So x = 2(4)

x = 8 [or -8]

4 and 8 are your answers. But if you think about it, -4 and -8 work too. Not sure how advanced your class is, but yeah, think about it.  -4^2 + -8^2 =  16 + 64 = 80  and -4 * 2 = -8. </PRE>