DETAILS
EPPDISCMATHS7.2.012.
MY NOTES
a. Define Z by the rule Z = n^2 - 3n for each integer n.
Suppose n and m are any integers such that F(n) = F(m). Substituting from the definition of F gives that n^2 - 3n = m^2 - 3m.
Solving this equation for n and simplifying the result gives that n = m.
Therefore, F is injective.
Show that F is not surjective. Counterexample:
Let m = 2.
For this value of m, the only number n with the property that F(n) = m is not an integer. Thus, F is not surjective.
b. Define G by the rule G(x) = 2 - 3x for each real number x.
Let y be any real number.
On a separate piece of paper, solve the equation y = 2 - 3x for x.
Enter the result in the box below.
(1) Is x a real number?
Sums, products, and differences of real numbers are real. Therefore, x is a real number.
(2) Does G(y) exist?
According to the formula that defines G, when G is applied to x, x is multiplied by 3 and the result is subtracted from 2.
When the expression for x that you found above is multiplied by 3, the result is 2 - 3x.
And when the result is subtracted from 2, you obtain y.
Thus, G(y) exists.