1.) If n is the element of natural numbers and n is a perfect square, then the units digit of n is not 2.

2.) If a,b is in the emement of natural numbers and both a and b are odd, then x^2+ax+b can not be factored into a product of two linear factors (a linear factor has the form cx+d, where c,d are elements of natural numbers)

3.) Prove by Induction

1+x+x^2+...+x^n=(x^(n+1)-1)/(x-1)