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Question Number 80643 by mr W last updated on 05/Feb/20

Prove that there is no solution for  7^n ≡1 mod(35) with n∈N.

Provethatthereisnosolutionfor7n1mod(35)withnN.

Answered by MJS last updated on 05/Feb/20

∀k∈N: 7^(20k) ≡1mod 55

kN:720k1mod55

Commented by mr W last updated on 05/Feb/20

thanks sir! i should have asked  7^n ≡1 mod (35). is there a solution?

thankssir!ishouldhaveasked7n1mod(35).isthereasolution?

Commented by MJS last updated on 05/Feb/20

no solution except n=0  k∈N^★ : 7^(4k) ≡21mod 35  k∈N:       7^(4k+1) ≡7mod 35       7^(4k+2) ≡14mod 35       7^(4k+3) ≡28mod 35

nosolutionexceptn=0kN:74k21mod35kN:74k+17mod3574k+214mod3574k+328mod35

Commented by mr W last updated on 05/Feb/20

thank you sir for confirming!

thankyousirforconfirming!

Answered by mind is power last updated on 05/Feb/20

only n=0  if n≥1⇒7∣7^n ,7∣35  if ∃n such 7^n =1(35)⇒  7^n =1+35k⇒  1=7(7^(n−1) −5k)⇒7∣1  absurd

onlyn=0ifn177n,735ifnsuch7n=1(35)7n=1+35k1=7(7n15k)71absurd

Commented by mr W last updated on 05/Feb/20

thanks alot sir! that′s it!

thanksalotsir!thatsit!

Commented by mind is power last updated on 05/Feb/20

y′re Welcom

yreWelcom

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