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I have what is supposed to be a curve:

$$25x^2 - 4y^2 = 100$$

When simplify this to be:

$$y = 2.5x - 5$$

it is a line.

But isn't it supposed to be the same?

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1 Answer

up vote 8 down vote accepted

It looks like you've gone from

$$25x^2-4y^2 = 100$$

to

$$5x-2y=10\;?$$

This is not a valid operation; the square root (or any other power) of a sum is not the sum of the square roots (or powers) of the individual terms.

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ouch, now I feel ashamed. Thank you! :) –  nighty Apr 26 '11 at 11:18
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No need to. Live and learn -- better to have tried and failed than never to have tried at all :-) –  joriki Apr 26 '11 at 11:20
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