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## Topic review (newest first)

bobbym
2012-10-14 21:11:05

Hi;

Yes, it is an obvious error, the answer can never exceed m. In either direction.

bob bundy
2012-10-14 21:08:00

My point was that Harold can eliminate obvious errors such as -43 on the grounds that it is out of range.

Bob

bobbym
2012-10-14 21:02:32

Hi Bob;

Good Morning.

That is what I am getting too.

bob bundy
2012-10-14 20:57:00

Good morning bobbym

Bob

bobbym
2012-10-14 20:37:55

Hi bob;

If you did that what do you get for -65 mod -17?

bob bundy
2012-10-14 18:51:07

The formula should always give a value x, so that -m < x < m (assuming m is positive ... reverse the signs otherwise)

Bob

bobbym
2012-10-13 22:49:15

Hi Harold;

Use a calculator to at least check.

Harold
2012-10-13 22:43:55

You're right,i missed a minus sign,thank you a lot,you guys taught me a lot of things today.

bobbym
2012-10-13 21:00:24

Hi;

I am getting

bob bundy
2012-10-13 20:47:16

Looks like -23 - 20 = -43 rather than -23 + 20 = -3

There are a lot of minus signs to take account of.  Easy to slip up on that.

Bob

bobbym
2012-10-13 20:24:25

Hi;

I am getting -3 as the answer. Can I see what you have done?

Harold
2012-10-13 19:30:24

I am sorry to bug again but after you gave me the formula,i experimented a little and solution to -23 mod -5 results -43,is it correct

bob bundy
2012-10-13 03:15:27

hi Harold,

In effect, that was my point in post 7.

The following are all equivalent mod 5

-12,  -7,  -2, 3, 8, 13, 18 ......

Basically just add 5.

If you follow my link to Wiki you will see that two definitions are possible and there are even more variations amongst computer languages.

Your brother is right using the 'Euclidean division' definition ... under this no negatives are allowed.

Which is why I think you need to check with your teacher / tutor and see what definition is required.

Bob

Harold
2012-10-13 02:21:18

Guys,I have another problem,my brother says that 23 mod -5 will be 3 as Euclidean division states a=bq+r and the division will be 23=(-5)*(-4)+3.

bobbym
2012-10-13 00:10:13

Hi;

Yes he has (in post 3).  He got -2

I see that now. He got the right answer too.

Sometimes it has to be the same sign as the divisor. I gave him the one that gets the same answers as Wolfram would.

Unfortunately he skeddadled right after he solved it. I wanted to go a little deeper.