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Home Q & A Board Science-Related Homework Help Mathematics
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Oc646 Oc646
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11 years ago
9x^2-4y^2=36
y= 3x-6

THANKS so much.  I got all my other problems.  Just confused about the 4y^2. Dont know what to do with it.

Slight Smile xoxo
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ObymbaezeObymbaeze
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11 years ago
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#2
11 years ago
This problem begs for substitution -- substituting 3x-6 for the y in the first equation:

9x^2 - 4(3x-6)^2 = 36

9x^2 -4(9x^2 -36x +36) = 36

9x^2 -36x^2 +144x -144 = 36

-27x^2 + 144x - 180 = 0, divide by -9

3x^2 - 16x + 20 = 0

(3x -10) (x - 2) = 0

x = 10/3 or x = 2

there ya go!  You've got two x's, plug in for y and you'll have two points, which makes sense.
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