If gcd(a,b)=1\gcd(a, b) = 1gcd(a,b)=1 (i.e., aaa and bbb are coprime), which statement must be true?
Both aaa and bbb are prime numbers
lcm(a,b)=a×b\text{lcm}(a, b) = a \times blcm(a,b)=a×b
a+ba + ba+b is prime
a×b=1a \times b = 1a×b=1