Exercise · ZW-LAW-OF-QUADRATIC-RECIPROCITY-005 · ★★☆ Intermediate
Compute \(\left(\frac{2}{7}\right)\).
Choose one option.
Show answer
- C. \(1\)
Explanation
Since \(7\equiv -1\pmod 8\), the supplement \(\left(\frac{2}{p}\right)\) equals 1. Hence \(\left(\frac{2}{7}\right)=1\), and 2 is a quadratic residue modulo 7.
Review the concept: Law of quadratic reciprocity
The law of quadratic reciprocity relates the Legendre symbols \(\left(\frac{p}{q}\right)\) and \(\left(\frac{q}{p}\right)\) for distinct odd primes \(p\) and \(q\).
\[\left(\frac{p}{q}\right)\left(\frac{q}{p}\right)=(-1)^{\frac{(p-1)(q-1)}{4}}\]
More practice problems: law of quadratic reciprocity
- ZW-LAW-OF-QUADRATIC-RECIPROCITY-001 State the law of quadratic reciprocity for distinct odd primes p and q.
- ZW-LAW-OF-QUADRATIC-RECIPROCITY-002 According to the law, when is ((p)/(q))((q)/(p))=-1?
- ZW-LAW-OF-QUADRATIC-RECIPROCITY-003 Compute ((3)/(5))((5)/(3)).
- ZW-LAW-OF-QUADRATIC-RECIPROCITY-004 What is the supplement formula for ((-1)/(p)) when p is an odd prime?
- ZW-LAW-OF-QUADRATIC-RECIPROCITY-006 Compute ((-1)/(7)).
- ZW-LAW-OF-QUADRATIC-RECIPROCITY-007 Compute ((5)/(11)).
- ZW-LAW-OF-QUADRATIC-RECIPROCITY-008 Does the congruence x^2≡ 3pmod11 have a solution?
- ZW-LAW-OF-QUADRATIC-RECIPROCITY-009 By definition, when is ((a)/(p))=0?
← ZW-LAW-OF-QUADRATIC-RECIPROCITY-004 ZW-LAW-OF-QUADRATIC-RECIPROCITY-006 →