1. Number-Unit digit 71−7 72−9 73−3 74−1 75−7 7174−(7)43×4−1×9=9 2. Let n is a add number then (n+2) is also a odd number, Now, (n+2)−(n)2=(2n+2).2 =4(n+1) As n is odd, so (n+1) is even number and must be divisible by 2 . Hencedifference of square of two odd number is away divisible by 8 .
3.Let n and (n+2) are two odd number, Now, n(n+2)+1=n2+2n+1=(n+1)2 This is perfect square Hence, statement 2 and 3 are true