If a2≡b2(modm)a^2 \equiv b^2 \pmod{m}a2≡b2(modm), which of the following is necessarily true?
a≡b(modm)a \equiv b \pmod{m}a≡b(modm) or a≡−b(modm)a \equiv -b \pmod{m}a≡−b(modm)
a≡b(modm)a \equiv b \pmod{m}a≡b(modm)
a2−b2a^2 - b^2a2−b2 is a multiple of mmm
a=ba = ba=b