SOLUTION: Hello, This is taken from a practice test (the answer they give is 2). I am not sure how to solve it. Can I use elimination? Thanks. <a href="http://s571.photobucket.com/us

Algebra ->  Graphs -> SOLUTION: Hello, This is taken from a practice test (the answer they give is 2). I am not sure how to solve it. Can I use elimination? Thanks. <a href="http://s571.photobucket.com/us      Log On


   

Question 823977: Hello,
This is taken from a practice test (the answer they give is 2).
I am not sure how to solve it. Can I use elimination?
Thanks.

photo 2013-12-21-a-1.jpg
Answer by jim_thompson5910(35256) About Me  (Show Source):
You can put this solution on YOUR website!
I'd use substitution.

Solve the second equation for y.

2x + y = 0

y = 0 - 2x

y = -2x

-------------------------------------------------------

Then plug it into the first equation

5x^2 + y^2 = 9

5x^2 + (-2x)^2 = 9 ... replace every copy of 'y' with '-2x' (since y = -2x)

5x^2 + 4x^2 = 9

9x^2 = 9

x^2 = 9/9

x^2 = 1

x = +-sqrt(1)

x = sqrt(1) or x = -sqrt(1)

x = 1 or x = -1


If x = 1, then...

y = -2x

y = -2*1

y = -2

Or...if x = -1, then ...

y = -2x

y = -2*(-1)

y = 2

So the values of y are y = -2 or y = 2

So the answer is choice c) 2