finding a point on an ellipse

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jmcmath
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finding a point on an ellipse

Postby jmcmath » Tue Nov 06, 2012 12:23 am

I have this question that I am stumped on, I have changed the numbers to a practice another version so that it is not the exact question on my homework.

An arch of a bridge is semielliptical, with major axis horizontal. The base of the arch is a across, and the highest part of the arch is b above the horizontal roadway, as shown in the figure. Find the height of the arch 7 feet from the center of the base. Assume a = 40 feet, b = 8 feet. (Round the answer to one decimal place.)

What I did..
wrote out my equation as (x^2/1600)+(y^2/64) = 1 from a^2 = 40^2 b^2 = 8^2
so i enter 7 in for x making it 49/1600 +y^2/64 = 1 that becomes sqrt ((1-49/1600) * 64)
that gives me the answer 7.9 however the answer key says 7.5 so where am i going wrong?

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stapel_eliz
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Postby stapel_eliz » Tue Nov 06, 2012 2:27 am

Maybe the answer key has a typo. I get your value. :wink:

jmcmath
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Re: finding a point on an ellipse

Postby jmcmath » Tue Nov 06, 2012 8:05 pm

noooo haha, :shock: now im so cunfused to why its counting my answer to the regular question wrong! i only have 3 tries! haha

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stapel_eliz
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Postby stapel_eliz » Tue Nov 06, 2012 10:52 pm

jmcmath wrote:noooo haha, :shock: now im so cunfused to why its counting my answer to the regular question wrong! i only have 3 tries! haha

I'm sorry, but I don't know what this means. :shock:

jmcmath
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Re: finding a point on an ellipse

Postby jmcmath » Wed Nov 07, 2012 3:42 pm

Its on an online homework site called webassign. after 3 tries you loose all points possible for the question, I have submitted 2 wrong answers so I only have 1 attempt left to get it correct! I really dont see whats flawed with this unless the homework answer is just incorrect

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stapel_eliz
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Postby stapel_eliz » Wed Nov 07, 2012 9:44 pm

jmcmath wrote:Its on an online homework site called webassign. after 3 tries you loose all points possible for the question, I have submitted 2 wrong answers so I only have 1 attempt left to get it correct! I really dont see whats flawed with this unless the homework answer is just incorrect

If you know the answer they want, why not give them that answer? Sure, it's wrong (assuming your posted question is correct), but at least you'll get the points. :wink:


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