Answer with Step-by-step explanation:
Let Z be a set of integers
We have to prove that 
is odd for all value of x 
Z.
There are two cases
1.When x is an odd integer number
2.when x is even integer number
1.When x is an odd integer number
When x is positive odd integer
Then 
is positive odd number (because square of odd positive number is always positive an odd number )
5x is also odd number
-5x -1 = -even number
Suppose x=3
Then -15-1=-16
Odd number - even number=Odd number
Hence , is an odd number .
When x is negative odd number
Then x square is positive odd number and 5x is negative odd term term
Therefore,odd number + odd number -1=Even number -1=Odd number
Hence 
is an odd number.
2.When x is an even number
When x is positive even number
x square is positive even number and 5x is positive even number
Even number -Even number -1 =Even number -odd number =Odd number
Suppose x=4
=16-20-1=-5=Odd number
When x is negative even number
Then x square is positive even number and 5x is negative even number
=Even number +Even number -1=Even number -1=Odd number
Hence, for all elements of Zis odd.
