Question

Angie did the following proof in her logic class. Which step in the indirect proof did she do incorrectly?

Prove: 8 is divisible by 4.
Step 1: Assume that 8 is not divisible by four.

Step 2: 8 is divisible by 4
Step 3: 8 is divisible by 4.
Step 1
Steps 1 and 3
Step 3
Step 2

Answer 1

i think c

Answer 2

@Tootles143 @Squirrels

Answer 3

I'm not good with math bro #sry

Answer 4

Bruh... This looks confusing... What is the point of the problem... Sorry not that good but trying. :'(

Answer 5

its either 3 or 2 is wrong

Answer 6

so c or d is correct

Answer 7

Idk...? I think A... Because she assumed... idk?

Answer 8

its proofs thats how proofs work

Answer 9

What ya mean? Sorry im slow... :p

Answer 10

its confusing

Answer 11

just wish ambius would tell me if im right or not

Answer 12

Are steps 2 and 3 supposed to be the same? I'm trying to follow the logic, and the steps don't seem very clear to me.

I'd say their are two possible answers, assuming step 2 is the assertion/conclusion that 8 is divisible by 4.

First solution:
(Step 1) is the initial proposition which is assumed to be true.
(Step 1 and 3) is the "incorrect step" because it is a contradiction
(Step 3) is the proof that 8 is indeed a contradiction to the original proposition, and therefore
(Step 2) is the solution

Answer 13

What he said... ^

Answer 14

so answer is?

Answer 15

Is there a "none of the above answer"?

Answer 16

Im just kidding... I think C...

Answer 17

The second answer could be:

(step 1 and 3) could be an attempt at showing the contradiction as a step using conjuction....

In which case, you would be correct as their would be no reason to assert that 8 is divisible by 4 a second time... honestly, I think the outline of the proof is slightly ambiguous.

Answer 18

In other words, in the one that me and tootles agreed on (Step 1 and Step 3) looks to be the incorrect step - in my first answer, that's generally how a proof is done.

However, given the information you have, there's also no reason why your answer is necessarily incorrect... there's more that one way to do a proof... however, most proofs follow a pattern.

proposition
proof (validation, contradiction, etc...)
assertion (or invalidation) of our original proposition, (potentially in favour of another)

I think it's a poorly worded question. If it's simply one multiple choice question, I would go with what your gut feeling is (after all, it's only 1 problem). If you go by your first answer, the contradiction to the original proposition is very clear (as 8 can't be both divisible by 4 and not divisible by 4 at the same time). If you come across a lot of problems like that, I'd ask the teacher what they are looking for.

Answer 19

it was step 2

Answer 20

so, me and tootles were right then... sry I couldn't clear it up for you any more, but there were aspects to the question that seemed vague to me.

Answer 21

So i was right? =O

Answer 22

u guys said 1 and 3

Answer 23

so thats what i put

Answer 24

No i said... C...

Answer 25

c is 3 not 2

Answer 26

Yeah i know...

Answer 27

correct answer was d. step 2

Answer 28

I was close... Sorry i wasnt f help... :'(

Answer 29

of*

Answer 30

it fine.geomitry is the stupidest subject known to man

Answer 31

Oh... True? I havent even reached geometry... -.-

Answer 32

it is just so complicated. i thought i was just gonne be making shapes