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.
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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.
Answer by jim_thompson5910(35256) (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
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