Proof

zee-f · 2012-12-12 00:06:57

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)

Bob · 2012-12-12 04:43:32

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

anonimnystefy · 2012-12-12 05:54:47

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.

zee-f · 2012-12-12 06:02:55

I answered A and it was incorrect .

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

zee-f · 2012-12-12 06:04:12

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

Bob · 2012-12-12 06:47:20

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

zee-f · 2012-12-12 07:29:35

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

Bob · 2012-12-12 08:11:35

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

Bob

zee-f · 2012-12-12 09:30:23

I am still confused on what am really doing

I got 6 incorrect out of 20

I choose A and it was incorrect
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

Bob · 2012-12-12 09:43:58

6/20 eeekkk!

Oh hang on. 6 wrong. 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

zee-f · 2012-12-12 12:36:58

yup 14/ 20

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

Bob · 2012-12-12 20:25:12

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

zee-f · 2012-12-13 05:15:48

no EJ ≠ Jm

zee-f · 2012-12-13 05:16:55

So B would be a good answer ?

Bob · 2012-12-13 06:06:32

Yes, that's what I would choose.

Bob

zee-f · 2012-12-13 07:10:51

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

Bob · 2012-12-13 07:21:16

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

zee-f · 2012-12-13 07:33:10

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

zee-f · 2012-12-13 07:34:26

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

Bob · 2012-12-13 07:46:55

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

Bob

zee-f · 2012-12-13 08:23:42

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

Bob · 2012-12-13 08:27:39

Yes. That's what I think.

Bob

zee-f · 2012-12-13 11:16:00

2 more left

I answered C for both it was incorrect

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

Bob · 2012-12-13 11:38:25

hi

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

I think you'll see what to do then.

Bob

zee-f · 2012-12-13 11:56:09

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

Math Is Fun Forum

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

Proof

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

Re: Proof

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

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