Answer:
Step-by-step explanation:
First we compute [tex]9^n[/tex], for [tex]n = 0,1,2,3,4,5[/tex]
[tex]9^0=1,9^1=9,9^2=81,9^3=729,9^4=6561,9^5=59049[/tex]
We have the unit digit of [tex]9^n[/tex], is either 1 or 9
Therefore, the conjecture can be state as follows
Conjecture; the unit of digit of [tex]9^n[/tex], is 1, when n is even and 9 when n is odd
Let the property p(n) be the formula;
"The unit digit of [tex]9^n[/tex], is 1 when n is even and 9 when n is odd"↔ P(n)
To show p(n) is true , we will use strong mathematical inductive
Show tgat p(0) and p(1) are true
We have to show the unit digit of [tex]9^0[/tex] is 1 and [tex]9^1[/tex] is 9
Since any integer with zero power is one and hence
[tex]9^0=1[/tex] and [tex]9^1 = 9[/tex]
Therefore, p(0) and p(1) are true
Show that for al integer [tex]k\geq 1[/tex], if p(i) is true for all integer i from o through k, then p(k+1) is also true
let k be any integer with [tex]k \geq 1[/tex] and suppose that for all integer i with [tex]0 \leq i \leq \leq k[/tex]
the unit digit of [tex]9^i[/tex] is 1 when is even and 9 when n is odd
we must show that [tex]9^{k +1}[/tex] equals 1 when n is even and 9 when n is odd
Case I; (k +1 is odd)
in this case k is even and so, by inductive hypothesis, the unit digit of [tex]9^k[/tex] is 1 and hence there is some non negative integer q such that
[tex]9^k = 10q + 1[/tex]
now, [tex]9^{k+1}=9^k(9)[/tex]
= (10q + 1)9
= 90q + 9
= 10.9q + 9
Note that for any non negative integer q , 9q is also an integer and this implies the unit digit of [tex]9^{k+1}[/tex] is 9
Case II
(k +1 is even)
in this case k is odd and so, by inductive hypothesis, the unit digit of [tex]9^k[/tex] is 9 and hence there is some non negative integer q such that
[tex]9^k=10q+9[/tex]
Now,
[tex]9^{k+1}=9^k.9\\=(10q+9)9\\=90q+81\\=10(9q+8)+1[/tex]
Note that any non negative integer q, 9q + 8 is also an integer and this implies the unit of [tex]9^{k+1}[/tex] is 1
Since we have proved both the basis and the inductive step of the strong mathematical induction, we conclude that the given statement is true
