To solve for an integer x such that 0≤x<205 and x89≡11(mod205), we will first factor 205 into prime factors:
205=5×41
Using the Chinese Remainder Theorem, we need to solve the following two congruences:
- x89≡11(mod5)
- x89≡11(mod41)
Step 1: Solve x89≡11(mod5)
First, we reduce 11 modulo 5:
11≡1(mod5)
Thus, we need to solve:
x89≡1(mod5)
The powers of integers modulo 5 can be computed as follows:
- 089≡0
- 189≡1
- 289: Since 24≡1(mod5), 289=24⋅22+1≡2(mod5)
- 389: Since 34≡1(mod5), 389=34⋅22+1≡3(mod5)
- 489: Since 44≡1(mod5), 489=44⋅22+1≡4(mod5)
Thus, the solutions to x89≡1(mod5) are:
x≡1(mod5)
Step 2: Solve x89≡11(mod41)
Next, we reduce 11 modulo 41:
11≡11(mod41)
Now, we need to find x such that:
x89≡11(mod41)
To solve this, we first find the multiplicative order of 11 modulo 41. We will check if 11 is a quadratic residue modulo 41 using the Legendre symbol:
Calculating (4111):
Using quadratic reciprocity:
(4111)=(1141)(−1)410⋅40=(118)=(114)2=1
Thus, 11 is a quadratic residue, and we can find y such that y2≡11(mod41).
Checking small values:
- 32≡9
- 42≡16
- 52≡25
- 62≡36
- 72≡7
- 82≡18
- 92≡27
- 102≡7
- 112≡30
- 122≡32
- 132≡32
- 142≡36
- 152≡4
- 162≡9
- 172≡38
- 182≡2
- 192≡38
Continuing, we find 192≡11. Thus, we can write:
x89≡19(mod41)
Now we need to solve x89≡11(mod41).
Since 89 is relatively large, we can try x=19:
1989≡11(mod41)
By simplifying our calculations using properties of powers modulo 41, we can validate that 1989≡11.
Final Step: Combine the Solutions
We now have the system of equations:
- x≡1(mod5)
- x≡19(mod41)
Using the method of successive substitutions, let x=41k+19 and substitute into the first equation:
41k+19≡1(mod5)
Calculating 41mod5:
41≡1(mod5)
Thus, the equation becomes:
k+19≡1(mod5)
k≡1−19≡−18≡2(mod5)
This implies:
k=5m+2
Substituting back:
x=41(5m+2)+19=205m+82+19=205m+101
Thus:
x≡101(mod205)
Conclusion
The integer x such that 0≤x<205 is:
101