Euler's theorem
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Euler's theorem
calccryptocalccrypto 1246373018|%e %b %Y, %H:%M %Z|agohover
(1)
7^2^2^2 \equiv 7^4^*^5^5^+^2 \equiv (7^4)^5^5*7^2 \equiv 1^5^5*7^2 \equiv 49 \equiv 9 (\mod 10)

can someone tell me why this part is true?

(2)
(7^4)^5^5*7^2 \equiv 1^5^5*7^2

how does the 7^4 come out?


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Last edited on 1246445898|%e %b %Y, %H:%M %Z|agohover By thornahawk + Show more
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Unfold Euler's theorem by calccryptocalccrypto, 1246373018|%e %b %Y, %H:%M %Z|agohover
Re: Euler's theorem
DarkerLineDarkerLine 1246375687|%e %b %Y, %H:%M %Z|agohover

7^4 \equiv 1 \pmod{10} is actually the meat of Euler's theorem, since 4 is φ(10). This means that whenever 74 occurs in an equivalence mod 10, we can substitute 1 for it: if 7^4 \equiv 1, then (7^4)^{55} \equiv 1^{55} (raising both sides to a power), and (7^4)^{55}\cdot 7^2 \equiv 1^{55}\cdot 7^2 (multiplying both sides by 72).

Another way to see it is this: taking things mod 10 is equivalent to finding the last digit of a number. When multiplying two large numbers (e.g. 74*72 = 2401*49), if all we care about is the last digit of the result, we don't need to know what the other digits of the numbers themselves are, so we might as well just multiply 1*9. This is exactly what we're doing here: the last digit of 74 is 1, so we replace 74 by 1 when doing a last-digit calculation.

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Unfold Re: Euler's theorem by DarkerLineDarkerLine, 1246375687|%e %b %Y, %H:%M %Z|agohover
Re: Euler's theorem
calccryptocalccrypto 1246400339|%e %b %Y, %H:%M %Z|agohover

so because 10 has 4 values comprime to it we can substitute 1 for it:7^4 \equiv 1?

¿¿¿que???


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Unfold Re: Euler's theorem by calccryptocalccrypto, 1246400339|%e %b %Y, %H:%M %Z|agohover
Re: Euler's theorem
graphmasturgraphmastur 1246401400|%e %b %Y, %H:%M %Z|agohover

Actually, when you ask someone "what" in spanish, as in what did you say, or what was that, you actually do Cómo.

As for the problem, I have no earthly idea. Power wise, the 7 to the 4th to the 55th, is 7 to the 59th. However, he said that 7 to the 4th is equal to 1, so I don't know.


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Unfold Re: Euler's theorem by graphmasturgraphmastur, 1246401400|%e %b %Y, %H:%M %Z|agohover
Re: Euler's theorem
WeregooseWeregoose 1246405079|%e %b %Y, %H:%M %Z|agohover

Modular arithmetic would be very useful knowledge, so you should read up on it. …Imagine a clock face with ten hours. Starting at 0:00/10:00, we then move forward 7^4 hours. What hour would that be?

Also, you might remember that the last digit of a number can be acquired with 10fPart(.1X). This immediately follows from 10fPart(X/10), which can act as a replacement for X-10int(X/10) – essentially, we're using X (mod 10).

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Unfold Re: Euler's theorem by WeregooseWeregoose, 1246405079|%e %b %Y, %H:%M %Z|agohover
Re: Euler's theorem
calccryptocalccrypto 1246410799|%e %b %Y, %H:%M %Z|agohover

yeah. i know that much, i think. the clock would be 7^4 mod 10, but no further


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Unfold Re: Euler's theorem by calccryptocalccrypto, 1246410799|%e %b %Y, %H:%M %Z|agohover
Re: Euler's theorem
Timothy FosterTimothy Foster 1246411149|%e %b %Y, %H:%M %Z|agohover

@graphmastur (74)55 = 7220 since (xa)b = xab.

If you multiplied to numbers of the same base, then you add the exponents. xa*xb = xa+b

Last edited on 1246411172|%e %b %Y, %H:%M %Z|agohover By Timothy Foster + Show more
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Unfold Re: Euler's theorem by Timothy FosterTimothy Foster, 1246411149|%e %b %Y, %H:%M %Z|agohover
Re: Euler's theorem
graphmasturgraphmastur 1246413419|%e %b %Y, %H:%M %Z|agohover

Right, and (X^a)^b = X^(a*b).

I just couldn't understand how 7^4 = 1.


"But sanctify the Lord God in your hearts, and always be ready to give a defense to everyone who asks you a reason for the hope that is in you, with meekness and fear;" ~ 1 Peter 3:15

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Unfold Re: Euler's theorem by graphmasturgraphmastur, 1246413419|%e %b %Y, %H:%M %Z|agohover
Re: Euler's theorem
Timothy FosterTimothy Foster 1246421284|%e %b %Y, %H:%M %Z|agohover

I have never seen modular arithmetic before, but it seems to imply the elementary idea of remainders in division. For example, you can say that (although it is misleading and simply not mathematically proper) 17/4 is 4 with a remainder of 1. Therefore, 17 mod 4 is 1. I do not have any idea if this is entirely correct. Upon research, it seems there is more to this than what I hypothesize.

In mod 10, this is easy. The equivalence is simply the last digit of the integer. 134 = 4 mod 10. Therefore, 74 = 2401, which in mod 10 is 1. This is how this equivalence is made above.

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Unfold Re: Euler's theorem by Timothy FosterTimothy Foster, 1246421284|%e %b %Y, %H:%M %Z|agohover
Re: Euler's theorem
calccryptocalccrypto 1246417128|%e %b %Y, %H:%M %Z|agohover

yeah. i always failed at spanish. thank goodness im finished with it though


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Unfold Re: Euler's theorem by calccryptocalccrypto, 1246417128|%e %b %Y, %H:%M %Z|agohover
Re: Euler's theorem
calccryptocalccrypto 1246417315|%e %b %Y, %H:%M %Z|agohover

what do you mean "occurs in an equivalence"?

and how would your explanation work with other numbers? im horribly inept at substitution for some reason


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Unfold Re: Euler's theorem by calccryptocalccrypto, 1246417315|%e %b %Y, %H:%M %Z|agohover
Re: Euler's theorem
DarkerLineDarkerLine 1246484945|%e %b %Y, %H:%M %Z|agohover

What I mean is that 74 obviously isn't equal to 1 — it's only equivalent to 1 mod 10. So you can substitute 1 for it, but only when you're working in mod 10.

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Re: Euler's theorem
calccryptocalccrypto 1246486812|%e %b %Y, %H:%M %Z|agohover

ah. i see now


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