Prove: For all positive integers n, the numbers 7n+ 5 and 7n+ 12 are relatively prime.
bezout's theorem :- two integer a and b are coprime if their exist integer u and v such that au+bv=1
let b = 7n+5 , a = 7n+12
(7n+12)=(7n+5)+7
(7n+5)= n(7)+5
7= 1(5)+2
5=2(2)+1
we now just go back
1=5-2(2)
= 5-2(7-1(5))
= 5-2(7)+2(5)
= -2(7)+3(5)
= -2(7)+3((7n+5)-n(7))
= -2(7)+3(7n+5)-3n(7)
= -(2+3n)(7)+3(7n+5)
= -(2+3n)((7n+12)-(7n+5))+3(7n+5)
= -(2+3n)(7n+12)+(2+3n)(7n+5)+3(7n+5)
= -(2+3n)(7n+12)+(5+3n)(7n+5)
therefore -(2+3n)(7n+12)+(5+3n)(7n+5)=1
u = -(2+3n) v= (5+3n)
since n is integer therefore u and v are integers by above theorem we can conclude that 7n+12 and 7n+5 are relatively prime.
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