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Discrete Math or modulus

  • Thread starter bphysics
  • Start date
  • #1
35
0

Homework Statement



Find the remainder of dividing 2(562009)-3.

Homework Equations



Let m be a positive integer. If a[tex]\equiv[/tex]b (mod m) and c[tex]\equiv[/tex]d (mod m), then a + c [tex]\equiv[/tex] b + d (mod m) and ac[tex]\equiv[/tex]bd (mod m).

The Attempt at a Solution



Using ac[tex]\equiv[/tex]bd (mod m):

(2 mod 55)(562009mod 55) - (3 mod 55)

Using a + c [tex]\equiv[/tex] b + d (mod m)

(2 mod 55)((552009 mod 55) + (12009 mod 55)) - (3 mod 55)

(2)(0+1)-(3) = -1 OR remainder of 54

This was a problem on my math test and I got 52 as the remainder at first, but it was wrong.

Thx if you can help me.
 

Answers and Replies

  • #2
Dick
Science Advisor
Homework Helper
26,258
618
54 is right, 52 is wrong. But your method is dubious. It looks like you are trying use a rule like (a+b)^n mod m=(a^n mod m)+(b^n mod m). That's not right. What is true is that a^n mod m=(a mod m)^n. Just use that 56 mod 55=1.
 
  • #3
35
0
Thanks so much =D, i'll remember that.
 

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