Discussion about math, puzzles, games and fun.   Useful symbols: ÷ × ½ √ ∞ ≠ ≤ ≥ ≈ ⇒ ± ∈ Δ θ ∴ ∑ ∫  π  -¹ ² ³ °

You are not logged in.

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

zee-f
Member
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

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

Offline

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

bob bundy
Registered: 2010-06-20
Posts: 8,462

### 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

Children are not defined by school ...........The Fonz
You cannot teach a man anything;  you can only help him find it within himself..........Galileo Galilei
Sometimes I deliberately make mistakes, just to test you!  …………….Bob Bundy

Offline

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

anonimnystefy
Real Member
From: Harlan's World
Registered: 2011-05-23
Posts: 16,039

### 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
The knowledge of some things as a function of age is a delta function.

Offline

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

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

### Re: Proof

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

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

Offline

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

zee-f
Member
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

Offline

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

bob bundy
Registered: 2010-06-20
Posts: 8,462

### 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

Children are not defined by school ...........The Fonz
You cannot teach a man anything;  you can only help him find it within himself..........Galileo Galilei
Sometimes I deliberately make mistakes, just to test you!  …………….Bob Bundy

Offline

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

zee-f
Member
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

Offline

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

bob bundy
Registered: 2010-06-20
Posts: 8,462

### Re: Proof

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

Bob

Children are not defined by school ...........The Fonz
You cannot teach a man anything;  you can only help him find it within himself..........Galileo Galilei
Sometimes I deliberately make mistakes, just to test you!  …………….Bob Bundy

Offline

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

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

### Re: Proof

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

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

Offline

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

bob bundy
Registered: 2010-06-20
Posts: 8,462

### Re: Proof

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

Children are not defined by school ...........The Fonz
You cannot teach a man anything;  you can only help him find it within himself..........Galileo Galilei
Sometimes I deliberately make mistakes, just to test you!  …………….Bob Bundy

Offline

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

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

### Re: Proof

yup 14/ 20

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

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

Offline

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

bob bundy
Registered: 2010-06-20
Posts: 8,462

### 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

Children are not defined by school ...........The Fonz
You cannot teach a man anything;  you can only help him find it within himself..........Galileo Galilei
Sometimes I deliberately make mistakes, just to test you!  …………….Bob Bundy

Offline

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

zee-f
Member
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

Offline

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

zee-f
Member
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

Offline

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

bob bundy
Registered: 2010-06-20
Posts: 8,462

### Re: Proof

Yes, that's what I would choose.

Bob

Children are not defined by school ...........The Fonz
You cannot teach a man anything;  you can only help him find it within himself..........Galileo Galilei
Sometimes I deliberately make mistakes, just to test you!  …………….Bob Bundy

Offline

## #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

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

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

Offline

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

bob bundy
Registered: 2010-06-20
Posts: 8,462

### 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

Children are not defined by school ...........The Fonz
You cannot teach a man anything;  you can only help him find it within himself..........Galileo Galilei
Sometimes I deliberately make mistakes, just to test you!  …………….Bob Bundy

Offline

## #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

Offline

## #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

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

Offline

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

bob bundy
Registered: 2010-06-20
Posts: 8,462

### Re: Proof

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

Bob

Children are not defined by school ...........The Fonz
You cannot teach a man anything;  you can only help him find it within himself..........Galileo Galilei
Sometimes I deliberately make mistakes, just to test you!  …………….Bob Bundy

Offline

## #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

Offline

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

bob bundy
Registered: 2010-06-20
Posts: 8,462

### Re: Proof

Yes.  That's what I think.

Bob

Children are not defined by school ...........The Fonz
You cannot teach a man anything;  you can only help him find it within himself..........Galileo Galilei
Sometimes I deliberately make mistakes, just to test you!  …………….Bob Bundy

Offline

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

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

### Re: Proof

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

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

Offline

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

bob bundy
Registered: 2010-06-20
Posts: 8,462

### 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

Children are not defined by school ...........The Fonz
You cannot teach a man anything;  you can only help him find it within himself..........Galileo Galilei
Sometimes I deliberately make mistakes, just to test you!  …………….Bob Bundy

Offline

## #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 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

Offline