Math Level II C Emergency questions : Letus Rectum

Archive SAT Subject Test Preparation
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<p>hey guys i desperately need to solve this stupid problem…</p>

<p>this is probably super easy for u guys but i somehow dont get it</p>

<p>here it is</p>

<p>Q : The length of the latus rectum of the hyperbola whose equation is
x^2 - 4y^2 = 16 is …</p>

<p>you know you have to change this form to some kind of ‘hyperbola form’ and you have to use 2b^2 / a …</p>

<p>I just don’t know how to change the form… i guess it’s making a ‘perfect square’. could you guys try tell me how to change this from to hyperbola form?? this is from barron’s… I dont even know i’m allowed to post this kind of question… :(</p>

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<p>i just read bottom thread about some of barrons questions not even on the actual exam</p>

<p>do i even have to know letus rectum ? hmm</p>

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<p>It goes into way too much detain in section 4.1. You don’t have to know all the nonsense about latus rectums and conjugate axes, etc. Know the basic equations for conic sections like the back of your hand, how to shift them, and maybe the bit about eccentricity, etc.</p>

<p>Aha!</p>

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<p>that was kinda like my question</p>

<p>i dont know how to shift them</p>

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<p>That, I will get back on.</p>

<p>I need to cram this week.</p>

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<p>no you don’t have to know that</p>

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<p>barron’s is stupid and the BIGGEST waste of time. EVER.</p>

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<p>^^Seriously.</p>

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<p>well i prepped from barron’s and my SAT IIC is in about 10 hours, and there isn’t much i can do about it now, except hope that the fricken book isnt really as bad as EVERYONE seems to think it is…WHY did i have to get barron’s to study from!!!</p>

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<p>siva, to answer your question;</p>

<p>if its an ellipse, you try get the RHS=1,so x^2 - 4y^2 = 16 becomes
((x^2)/16)-((4y^2)/16)=1</p>

<p>(x^2/4^2)-(y^2/2^2)=1</p>

<p>so a=4. b=2.
therefore latus rectum= 2b^2/a= 2x2^2/4=8/4=2(Ans).</p>

<p>hope i made things simpler.</p>

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<p>oops, i meant hyperbola, not ellipse…hehe.</p>

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<p>thanks for the response</p>

<p>but what dpes RHS mean??</p>

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<p>do u just divide to make it equal to 1?</p>

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<p>RHS= Right Hand Side. Divide both sides by 16, so of course 16/16=1</p>