Answer:
Step-by-step explanation:
<u>Given system:</u>
<u>Add up equations:</u>
<u>Find y:</u>
Solution given:
x+y=12......[1]
x-y=6........[2]
adding equation 1 and 2 we get
x+y+x-y=12+6
2x=18
x=18/2
x=9
substituting value of x in equation 1
9+y=12
y=12-9
y=3
I suppose the claim is for .
When , we have , and of course 5 divides 5.
Assume the claim holds for , that . We want to use this to show it holds for , that .
We have
Since , we can write for some integer . Then
which is clearly divisible by 5. QED
873 + 40 + 7 or 870 + 40 + 3 + 7