1.) Perimeter of rectangle with base B and Height H.
Perimeter =  2*(Base + Height)
 
                =  2*(B + H)
2.) Nth odd number.
Odd number sequence = 1, 3, 5, 7, 9, 11, ........
                                                             (2n + 1)
zeroth, 0th, odd number = 1                     2*0 + 1 = 1     
1st odd number = 3                                2*1 + 1 = 3 
2nd odd number = 5                               2*2 + 1 = 5 
3rd odd number = 7                                2*3 + 1 = 7 
4th odd number = 9                                2*4 + 1 = 9
And so on.   So the nth odd number starting from 0 is  = 2n + 1. 
                   
3.) Area of triangle with Base B and Height H
    Area = (1/2)*B*H  = (1/2)BH