SOLUTION: Let f∶ Z×Z→Z×Z be defined as f(m,n)=(3m+7n,2m+5n). Is f a bijection, i.e., oneto-one and onto? If yes then give a formal proof, based on the definitions of

Algebra ->  Functions -> SOLUTION: Let f∶ Z×Z→Z×Z be defined as f(m,n)=(3m+7n,2m+5n). Is f a bijection, i.e., oneto-one and onto? If yes then give a formal proof, based on the definitions of       Log On


   



Question 1074818: Let f∶ Z×Z→Z×Z be defined as f(m,n)=(3m+7n,2m+5n). Is f a bijection, i.e., oneto-one and onto? If yes then give a formal proof, based on the definitions of one-to-one and onto, and derive a formula for f−1. If no then explain why not.
Answer by Fombitz(32388) About Me  (Show Source):
You can put this solution on YOUR website!
No, the function is not one-to-one.
f%28a%2Cb%29=(3a%2B7b,2a%2B5b)
f%28c%2Cd%29=(3c%2B7d,2c%2B5b)
So if the function is one-to-one,
f%28a%2Cb%29=f%28c%2Cd%29 implies that a=c and b=d.
Just looking at the first component,
3a%2B7b=3c%2B7d
Let's assume b=c=0
Then,
3a=7d
a=%287%2F3%29d
So, a%3C%3Ec and f is not one-to-one.