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#1 2012-12-12 00:06:57

zee-f
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Registered: 2011-05-12
Posts: 1,220

Proof

Hi,

I really need help seeing if I answered the following correct:


I'll give you an assumption, and ask you to provide proof for the assumption.  If there is no proof for the assumption, the answer is "unfounded."

I choose A

1. If I have two coplanar lines, I must have a plane.

A-unfounded
B-Definition of a point
C-Definition of a plane
D-Given
E -Definition of a line
F -Definition of radius

Last edited by zee-f (2012-12-12 00:41:33)


One, who adopts patience, will never be deprived of success though it may take a long time to reach him. Imam ali (as)<3

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#2 2012-12-12 04:43:32

bob bundy
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Registered: 2010-06-20
Posts: 6,297

Re: Proof

hi zee-f,

I think this can be proved.  Isn't a plane defined by 3 (non-colinear ) points?

How could you find 3 such points on those two lines?   

But I don't understand how you can prove that with just a letter.  Have you got any examples of this sort of thing?

Bob


You cannot teach a man anything;  you can only help him find it within himself..........Galileo Galilei

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#3 2012-12-12 05:54:47

anonimnystefy
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Registered: 2011-05-23
Posts: 15,315

Re: Proof

A is correct.

The statement isn't even true. Two lines that are actually the same line do not define a single plane, but are coplanar.


“Here lies the reader who will never open this book. He is forever dead.

“Taking a new step, uttering a new word, is what people fear most.” ― Fyodor Dostoyevsky, Crime and Punishment

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#4 2012-12-12 06:02:55

zee-f
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Registered: 2011-05-12
Posts: 1,220

Re: Proof

I answered A and it was incorrect neutral.

Yeah  this lesson is confusing but I did answer 14 correctly like this one :
(F ) was correct

6. In the figure above, line segment MC is equal to imaginary line segment MI.

A Given
Bunfounded
CDefinition of supplementary angles
D1267200 inches
E Definition of an octagon
F Definition of a circle: all points are equidistant from the center


One, who adopts patience, will never be deprived of success though it may take a long time to reach him. Imam ali (as)<3

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#5 2012-12-12 06:04:12

zee-f
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Registered: 2011-05-12
Posts: 1,220

Re: Proof

I have to use the information I know to proof the statement correct


One, who adopts patience, will never be deprived of success though it may take a long time to reach him. Imam ali (as)<3

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#6 2012-12-12 06:47:20

bob bundy
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Registered: 2010-06-20
Posts: 6,297

Re: Proof

stefy wrote:

Two lines that are actually the same line do not define a single plane, but are coplanar.

I did consider this, but rejected this interpretation on the grounds that 'two lines' should mean exactly two distinct lines not one line counted twice.

That's the trouble with using English to make mathematical statements.  It sometimes isn't precise enough.

As zee-f has had A marked wrong, I think we have further evidence that the questioner was thinking that way too.

So let's assume the lines are either (i) distinct and parallel or (ii) they cross at a point

So we either have 4 distinct points or at least 3.

What do we need to define a plane?

Bob


You cannot teach a man anything;  you can only help him find it within himself..........Galileo Galilei

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#7 2012-12-12 07:29:35

zee-f
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Registered: 2011-05-12
Posts: 1,220

Re: Proof

Hi,

According to my online courses  A plane is defined by any of the following:

three points not lying on a line
a line and a point not lying on the line
two lines which intersect in a single point or are parallel


So I think C would be a correct answer


One, who adopts patience, will never be deprived of success though it may take a long time to reach him. Imam ali (as)<3

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#8 2012-12-12 08:11:35

bob bundy
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Registered: 2010-06-20
Posts: 6,297

Re: Proof

Yes, C sounds good.  But I thought you had to supply the proof as well.  Maybe not.

Bob


You cannot teach a man anything;  you can only help him find it within himself..........Galileo Galilei

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#9 2012-12-12 09:30:23

zee-f
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Registered: 2011-05-12
Posts: 1,220

Re: Proof

I am still confused on what am really doing hmm

I got 6 incorrect out of 20 yikes

I choose A and it was incorrect sad
7. In the figure above, line segment EJ is equal to line segment JM

A Definition of radius
Bunfounded
CDefinition of an octagon
D1267200 inches
E Given
F Definition of supplementary angles


One, who adopts patience, will never be deprived of success though it may take a long time to reach him. Imam ali (as)<3

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#10 2012-12-12 09:43:58

bob bundy
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Registered: 2010-06-20
Posts: 6,297

Re: Proof

6/20 eeekkk!

Oh hang on.  6 wrong.  smile Oh that's not so bad.  70% is a good score.

But we'll get them sorted.  Don't worry.

I need to see the diagram for this one.

bob


You cannot teach a man anything;  you can only help him find it within himself..........Galileo Galilei

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#11 2012-12-12 12:36:58

zee-f
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Registered: 2011-05-12
Posts: 1,220

Re: Proof

yup 14/ 20 sad

The lesson uses the same chart for all the questions that use the chart

View Image: imageQ28.JPG

One, who adopts patience, will never be deprived of success though it may take a long time to reach him. Imam ali (as)<3

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#12 2012-12-12 20:25:12

bob bundy
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Registered: 2010-06-20
Posts: 6,297

Re: Proof

hi zee-f,

Oh, that diagram.  I remember that from another set of questions.

So EJ = JM ?  They're not telling that; they're asking is it true?

Take a look at the diagram.  Is J half way along EM ?

Bob


You cannot teach a man anything;  you can only help him find it within himself..........Galileo Galilei

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#13 2012-12-13 05:15:48

zee-f
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Registered: 2011-05-12
Posts: 1,220

Re: Proof

no EJ ≠ Jm


One, who adopts patience, will never be deprived of success though it may take a long time to reach him. Imam ali (as)<3

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#14 2012-12-13 05:16:55

zee-f
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Registered: 2011-05-12
Posts: 1,220

Re: Proof

So B would be a good answer ?


One, who adopts patience, will never be deprived of success though it may take a long time to reach him. Imam ali (as)<3

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#15 2012-12-13 06:06:32

bob bundy
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Posts: 6,297

Re: Proof

Yes, that's what I would choose.

Bob


You cannot teach a man anything;  you can only help him find it within himself..........Galileo Galilei

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#16 2012-12-13 07:10:51

zee-f
Member
Registered: 2011-05-12
Posts: 1,220

Re: Proof

I choose E and it was incorrect

my new answer is D
14. If a central angle is 30 degrees, then the arc it defines is also 30 degrees.

A Given
BDefinition of an inscribed angle
Cunfounded
DProperties of a central angle
E Properties of an arc
F Definition of radius


One, who adopts patience, will never be deprived of success though it may take a long time to reach him. Imam ali (as)<3

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#17 2012-12-13 07:21:16

bob bundy
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Registered: 2010-06-20
Posts: 6,297

Re: Proof

I see why you said E to start with.  I would say that D and E are the same.  But if E isn't acceptable, D seems good to me.

Bob


You cannot teach a man anything;  you can only help him find it within himself..........Galileo Galilei

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#18 2012-12-13 07:33:10

zee-f
Member
Registered: 2011-05-12
Posts: 1,220

Re: Proof

yeah I was stuck on which one to choose to. lol


One, who adopts patience, will never be deprived of success though it may take a long time to reach him. Imam ali (as)<3

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#19 2012-12-13 07:34:26

zee-f
Member
Registered: 2011-05-12
Posts: 1,220

Re: Proof

E was incorrect I still don't see why O_o

16. If a radius bisects a chord, then the lengths of the parts of the radius on either side of the chord are equal.

A Given
BDefinition of a chord
Cunfounded
DDefinition of supplementary angles
E Definition of a bisector
F Definition of radius


One, who adopts patience, will never be deprived of success though it may take a long time to reach him. Imam ali (as)<3

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#20 2012-12-13 07:46:55

bob bundy
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Registered: 2010-06-20
Posts: 6,297

Re: Proof

I think my diagrams will show you what to do here.

Bob

View Image: zeef proof.gif

You cannot teach a man anything;  you can only help him find it within himself..........Galileo Galilei

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#21 2012-12-13 08:23:42

zee-f
Member
Registered: 2011-05-12
Posts: 1,220

Re: Proof

No the radius isn't cut into equal parts so that whole statement is incorrect So C would be a good answer


One, who adopts patience, will never be deprived of success though it may take a long time to reach him. Imam ali (as)<3

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#22 2012-12-13 08:27:39

bob bundy
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Registered: 2010-06-20
Posts: 6,297

Re: Proof

Yes.  That's what I think.

Bob


You cannot teach a man anything;  you can only help him find it within himself..........Galileo Galilei

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#23 2012-12-13 11:16:00

zee-f
Member
Registered: 2011-05-12
Posts: 1,220

Re: Proof

2 more left  big_smile

I answered C for both it was incorrect neutral

19. The given points (4, -8), (4, -5), and (-2, -6) make a right triangle.
A Distance Formula
B Definition of a right triangle
CDefinition of a triangle
Dunfounded
E Pythagorean Theorem
F Definition of radius


20. The given points (2, -3), (-7, -7), (2, -7), and (-7, -2) make a square.
A Definition of coordinate
BPythagorean Theorem
CDefinition of a square
DDefinition of supplementary angles
E Distance Formula
F unfounded


One, who adopts patience, will never be deprived of success though it may take a long time to reach him. Imam ali (as)<3

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#24 2012-12-13 11:38:25

bob bundy
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Registered: 2010-06-20
Posts: 6,297

Re: Proof

hi

Did you try plotting the points?  Have a look at my diagram.

I think you'll see what to do then.

Bob

View Image: zeef proof2.gif

You cannot teach a man anything;  you can only help him find it within himself..........Galileo Galilei

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#25 2012-12-13 11:56:09

zee-f
Member
Registered: 2011-05-12
Posts: 1,220

Re: Proof

No I didn't plot them neutral probably why I got the question wrong the don't make a square or a right triangle So both (unfounded)


One, who adopts patience, will never be deprived of success though it may take a long time to reach him. Imam ali (as)<3

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